We should call methods with `.method_name` not `::method_name`. Fix two
instances of `YAML::load` I found in favor of `YAML.load`.

Delete default configuration

Because of this default configuration we're constantly checking if the
database exists when looping through configurations. This is unnecessary
and we should just delete it before we need to loop through
configurations.

Although not a direct dependency, it's pulled in by Resque for
Active Job integration tests so we need to update because the
rack-protection gem has a security vulnerability[1].

[1]: https://nvd.nist.gov/vuln/detail/CVE-2018-7212

Only us-east-1 gives URLs like bucket.s3.amazonaws.com whereas other
regions have URLs like s3-eu-west-1.amazonaws.com/ubxd-rails

CI with `jruby-head` compatible with Ruby 2.4.1

Since #32034 Rails 6 requires Ruby 2.4.1 or higher.
Two CI jobs configured with the latest version of`jruby-9.1.15.0`
compatibile with Ruby 2.3.3 are getting errors:

https://travis-ci.org/rails/rails/jobs/343519339

```
Bundler could not find compatible versions for gem "ruby":
  In Gemfile:
    ruby java
    rails java was resolved to 6.0.0.alpha, which depends on
      ruby (>= 2.4.1) java
Could not find gem 'ruby (>= 2.4.1)', which is required by gem 'rails', in any
of the relevant sources:
```

Improve ActiveJob custom argument serializers #30941

Ensure that `mini_magick` is absent after `rails new` with `--skip-active-storage`

Remove redundant assertions of an absence of `mini_magick` in `Gemfile`
since `bin/rails app:update` does not update Gemfile.
This assertions was added by 4a835aa3,
after reviewing of https://github.com/rails/rails/pull/32049 i realized
that assertions are redundant.

Remove `AS::Multibyte`'s unicode table

Avoid method_redefined warnings in  RouteSet::NamedRouteCollection

Fix generation of empty content security policy

Before:
```
~/.rbenv/versions/2.5.0/bin/ruby -w -Itest -Ilib -I../activesupport/lib -I../actionpack/lib -I../actionview/lib -I../activemodel/lib test/application/routing_test.rb
Run options: --seed 5851

.......~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:156: warning: method redefined; discarding old custom_path
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:321: warning: previous definition of custom_path was here
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:162: warning: method redefined; discarding old custom_url
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:321: warning: previous definition of custom_url was here
....~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:156: warning: method redefined; discarding old custom_path
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:321: warning: previous definition of custom_path was here
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:162: warning: method redefined; discarding old custom_url
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:321: warning: previous definition of custom_url was here
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:156: warning: method redefined; discarding old custom_path
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:321: warning: previous definition of custom_path was here
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:162: warning: method redefined; discarding old custom_url
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:321: warning: previous definition of custom_url was here
..........~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:156: warning: method redefined; discarding old custom_path
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:321: warning: previous definition of custom_path was here
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:162: warning: method redefined; discarding old custom_url
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:321: warning: previous definition of custom_url was here
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:156: warning: method redefined; discarding old custom_path
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:321: warning: previous definition of custom_path was here
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:162: warning: method redefined; discarding old custom_url
~/code/rails/actionpack/lib/action_dispatch/routing/route_set.rb:321: warning: previous definition of custom_url was here
.....

Finished in 13.233638s, 1.9647 runs/s, 5.8185 assertions/s.
26 runs, 77 assertions, 0 failures, 0 errors, 0 skips
```

After:
```
~/.rbenv/versions/2.5.0/bin/ruby -w -Itest -Ilib -I../activesupport/lib -I../actionpack/lib -I../actionview/lib -I../activemodel/lib test/application/routing_test.rb
Run options: --seed 38072

..........................

Finished in 12.009632s, 2.1649 runs/s, 6.4115 assertions/s.
26 runs, 77 assertions, 0 failures, 0 errors, 0 skips
```

Return all mappings for a timezone id in country_zones

Although the spec[1] is defined in such a way that a trailing semi-colon
is valid it also doesn't allow a semi-colon by itself to indicate an
empty policy. Therefore it's easier (and valid) just to omit it rather
than to detect whether the policy is empty or not.

[1]: https://www.w3.org/TR/CSP2/#policy-syntax

Setting up the request environment was accidentally creating a CSP
as a consequence of accessing the option - only set the instance
variable if a block is passed.

This reverts commit 86f7c269, reversing
changes made to 5ece2e4a.

If a policy is set then we should generate it even if it's empty.
However what is happening is that we're accidentally generating an
empty policy when the initializer is commented out by default.

Some timezones like `Europe/London` have multiple mappings in
`ActiveSupport::TimeZone::MAPPING` so return all of them instead
of the first one found by using `Hash#value`. e.g:

  # Before
  ActiveSupport::TimeZone.country_zones("GB") # => ["Edinburgh"]

  # After
  ActiveSupport::TimeZone.country_zones("GB") # => ["Edinburgh", "London"]

Fixes #31668.

rubocop single space after assignment

Fixes #32021.

The purpose of keeping app/views folder in API apps is that it's used for
mailer views so doesn't makes sense to keep it when Action Mailer is skipped.

* Don't use :: for class methods, we don't do that elsewhere.

* Don't install a needless method on minitest. Prefer assigning the
  reporter anyway as that's what minitest does internally.

* Don't bother opting out when the reporter ain't a Minitest::CompositeReporter.
  It's hardcoded: https://github.com/seattlerb/minitest/blob/005a3ba42c07d04797e2d00ac2c53e3be127c12f/lib/minitest.rb#L125
  And overrides have to create delegate reporters:
  https://github.com/kern/minitest-reporters/blob/1018b1b42f34b01d4de179c8aad2fa06771fe9b0/lib/minitest/minitest_reporter_plugin.rb#L72

Skip generating empty CSP header when no policy is configured

`Rails.application.config.content_security_policy` is configured with no
policies by default. In this case, Content-Security-Policy header should
not be generated instead of generating the header with no directives.
Firefox also warns "Content Security Policy: Couldn't process unknown
directive ''".

3acc5d6e was changed the order of scope evaluation from through scope to
the association's own scope to be prioritized over the through scope.
But the sorting order will be prioritized that is evaluated first. It is
unintentional effect, association scope's sorting order should be
prioritized as well.

Fixes #32008.

Fix active_job_basics.md callbacks example [ci skip]

This reverts commit cf4f05a7.

Since Rails 6 requires Ruby 2.4.1+.

So `2.4` would match `2.4.1` (due to an rvm alias) rather than matching
the latest `2.4.3` release.

This faithfully preserves grapheme clusters (characters composed of other
characters and combining marks) and other multibyte characters.