Fix `unscope` when an `eq` node which has no arel attribute

Update maintenance policy on security releases

This fixes a regression #38532 caused by f9633cd0.

Closes #38532.

Add guide for inline around_action

* Allow system tests using Rack::Test to run without Chrome

If you require "action_dispatch/system_test_case", the driven_by method
will be executed immediately.

* https://github.com/rails/rails/blob/v6.0.0/actionpack/lib/action_dispatch/system_test_case.rb#L162

Then the preload method is called in SystemTesting::Driver#initialize.

* https://github.com/rails/rails/blob/v6.0.0/actionpack/lib/action_dispatch/system_testing/driver.rb#L13
* https://github.com/rails/rails/blob/v6.0.0/actionpack/lib/action_dispatch/system_testing/browser.rb#L46-L63

Therefore, a "Webdrivers::BrowserNotFound" error occurs in the browser
preloading when you run system tests witout Chrome.

This commit avoid the error by lazy configuring the driver.

ref: #37410

* Don't preload the browser with :rack_test

If users specify `driven_by(:rack_test)`, it uses Chrome by default arguments.
However, `Rack::Test` does not use a browser and does not need to be preloaded.

Furthermore, it occurs `Webdrivers::BrowserNotFound` when run in
a container (or a machine) without Chrome.

If they are not included in this "test types" list, they're counted
towards app code lines, not test lines.

Merge pull request #38444 from eileencodes/add-schema-cache-tests-and-fix-one-more-bug

Adds some missing schema cache tests from master.

This reverts commit 7aa047b5, reversing
changes made to c9b36dd6.

This is a right example for singular names.

Registered predicate handler should be used for association queries

`OID` type should accept a value range of unsigned integers

Fix load_additional_types handling of large OIDs

This was introduced in https://github.com/rails/rails/pull/20559 but was wrongly asserting %w[close] to match close as the header value

Rack updated the RFC they're adhering to when parsing cookies, now no
longer including commas.

There's still an open question as mentioned in:
https://github.com/rails/rails/issues/38420

However, the resilience test is no longer as well needed as it once was
and we can move forward separately. If not, this is easily revertible.

Fix ActiveJob Test adapter not respecting retry attempts:

Fix Active Record `find_by_sql` doc example [ci skip]

There is a client that does not insert space before Mime Type parameter.
Ex. Salesforce OData client sends
`application/json;odata.metadata=full`. This commit allows Mime Type
string that does not have space before parameter.

The regex was introduced by
https://github.com/rails/rails/commit/ab38aa45497a38bc4a97f5eca430d43989f0b124

Fix grammar and diction of NOR conditions warning message

Update "Eagerly Requiring Helpers" section in testing docs [ci skip]

Skip keeps option shouldn't restrict from creating empty directories

Correct test helpers paths in test guides [ci skip]

Fix IRB deprecation warning on tab-completion on Ruby <= 2.5:

Fix IRB deprecation warning on tab-completion

`lib` isn't autoloaded in most applications and I wouldn't recomment
storing test helpers there even if it was.

This was brought up in #38343. I think the original author meant to
write `test/lib`. I updated the docs to say to use either `test/lib` or
`test/test_helpers` (personally I prefer the latter).

Ref https://github.com/ruby/ruby/pull/2857.

Force connected_to to load the records if it's a Relation

Regexp-escape table name for MS SQL

I'm not sure why #38316 includes this partly change for #36589, but I
suspect that is to sync method signature for the previous backport which
wrongly changed the `remove` method signature.

https://github.com/rails/rails/commit/9a400d808bdbebd5ea50cebc79bde591d2669017#diff-21d4fbe002689dc4b0ab29f021585457R624

That was not intended, so I'll revert both changes in 6-0-stable.

#37168 is not backported to 6-0-stable.

[ci skip]

Expose `klass.default_scoped` as public API

Fix fallout from recent back ports

* there's no connection_db_config in Rails 6.0
* remove_column and friends "options" changes.
* merge conflict markers in activerecord/CHANGELOG.md

Noticed while running tests for JRuby's AR-JDBC. While the Rails tests
where running fine, our local ones broke during migration tests.
Fixes are basically from master.

Fixes #38315