The tmp directory is added to version control in the newly created
application. This was added in Rails 5.0.0(https://github.com/rails/rails/commit/f06ce4c12a396795a3b2c1812951d9277bcb3a82).

However, applications created before that are not guaranteed to have the
tmp directory. If the tmp directory does not exist, writing to the key file
raise error.

This is a bit incompatible. So I fixed that create the directory before
writing a key.

support slice assignment on SafeBuffer

This was missed in the security fix for local dev. CI doesn't have a tmp
directory in the apps built for testing so these end up failing. This
adds the secret_key_base so we don't need to generate one.

We need to create a secret token in the application so that the travis
build doesn't error when trying to create a file in the tmp directory.

Fixes https://travis-ci.org/rails/rails/jobs/505908163#L6811

This reverts commit 65f2eeaa.

v6.0.0.beta3 release

[skip ci] Rails 5.1+ supports bigint primary key

Follow up #35573

This commit addresses the issue in
https://github.com/rails/rails/issues/35543 by making note of the
growing primary key issue with `create_or_find_by`.

Schema Cache: cache table indexes

Useful to not query for indexes when an application uses schema cache.

Ref https://github.com/rails/rails/pull/35546

Not looking for other contributions like this, but I took the liberty
since I was already working on this.

Update URL in RELEASING_RAILS.md [ci skip]

YAML has been used to serialize the schema cache ever since 2016 with
Rails 5.1: 4c00c6ed

* Update valid link for `signing release tag` from `git-scm` book
* Use `en`(English) instead of `tr`(Turkish) documentation link

The `Row` class is no longer used since d956772b.

Staled `@default_timezone` would cause an error on `reconnect!` after
`disconnect!`.

https://buildkite.com/rails/rails/builds/59495#23be8079-3a4f-4375-9991-0a6f874554f2

Steps to reproduce:

```
% ARCONN=postgresql bin/test test/cases/adapter_test.rb test/cases/base_test.rb -n "/(?:test_attributes_on_dummy_time|test_reconnect_after_a_disconnect)$/" --seed 15849
Using postgresql
Run options: -n "/(?:test_attributes_on_dummy_time|test_reconnect_after_a_disconnect)$/" --seed 15849

# Running:

.
E

Error:
ActiveRecord::AdapterTestWithoutTransaction#test_reconnect_after_a_disconnect:
NoMethodError: undefined method `add_coder' for #<PG::TypeMapAllStrings:0x00007f85ab9dd5b8>
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:866:in `update_typemap_for_default_timezone'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:652:in `exec_no_cache'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:636:in `execute_and_clear'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:894:in `add_pg_decoders'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:744:in `connect'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:285:in `rescue in block in reconnect!'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:281:in `block in reconnect!'
    /Users/kamipo/.rbenv/versions/2.6.1/lib/ruby/2.6.0/monitor.rb:230:in `mon_synchronize'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:280:in `reconnect!'
    /Users/kamipo/src/github.com/rails/rails/activerecord/test/cases/adapter_test.rb:465:in `block in <class:AdapterTestWithoutTransaction>'
```

Edit a changelog entry [ci skip]

Add additional ERB DummyCompiler tests

Change wording of some instances of 'opt out' [ci skip]

Update small typo in documentation.

This adds a few additional tests to the commits by eileencodes (https://github.com/rails/rails/pull/35497) and rafaelfranca (https://github.com/rails/rails/commit/cfa22f1a4b5e8b95ee01a432168de2f831b3f788). The additional tests cover several more ERB tag formatting cases such as multiline tags, conditional statements that result in duplicate keys, and multiple erb statements on a single line.

Show friendly message to install action mailbox if the related table does not exist

- This is similar to the work done in https://github.com/rails/rails/pull/31534

Fix warnings from Guides generation

After https://github.com/rails/rails/pull/35281  and https://github.com/rails/rails/pull/35036 AV warns about not having the compiled container.
Use the suggested with_empty_template_cache to overcome warning

Add note about has_many associations callbacks [ci skip]

Add a note explaining when the has_many associations callbacks will be called or not.

Add changelog entry for transliterate/parameterize accepting `locale` [ci skip]