It is in the code to provides backward compatibility for people that
have this class serialized as YAML in some storage.

Closes #22681

Remove unused `test/schema/mysql_specific_schema.rb`

Update README.md

Follow up to #22642.

Also, added a test case to make sure that the default deprecation horizon is
always bigger than the current Rails version.

Remove .DS_Store

Fix cache fetch miss notification order

Add No Doc

Remove blank line generated in config.ru

[ActionCable] declare asset_logged private

Explain what initializer/config_serializer does

Follow the lines of the other `.tt` files ([example](https://github.com/rails/rails/blob/1611ab4db173a7596a7a94c58dabf1483f070304/railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt#L26)) that have the space after the
condition to avoid too many white lines in the resulted file.

In reference to rails/rail#22403 add a :nodoc:

In line with the other initializers, add a short comment that explains
what happens when you change the value of the initializer.

[ci skip]

initializers/cookies_serializer is not new to 5.0

[ci skip]

The initializer has existed since 4.1, for instance see:
https://github.com/rails/rails/blob/v4.1.0/railties/lib/rails/generators/rails/app/templates/config/initializers/cookies_serializer.rb

Merge pull request #19423 from yuroyoro/fix_performance_regression_of_preloading_has_many_through_relation

Fix #12537 performance regression when preloading has_many_through association

fix typo in config value [ci skip]

Fix typo in CHANGELOG

wrapping i18n missing keys made optional

`I18n.translate` helper will wrap the missing translation keys
in a <span> tag only if `debug_missing_translation` configuration has
a truthy value. Default value is `true`. For example in `application.rb`:

    # in order to turn off missing key wrapping
    config.action_view.debug_missing_translation = false

🎉 🍻

Fix `receive` spelling

Handle specified schemas when removing a Postgres index

[ActionCable] Test invalid action on channel

Found `recieve` next to the correctly spelled method name, fixed it.

Also we prefer a one space padding within hashes, add that.

[ActionCable] test perform action with default action

This test needs to have a require for the Listen gem or else it returns
an error when run by itself or with a certain order in the Active
Support tests. We use `silence_warnings` because Listen has some
warnings about private methods. It's already silenced when it's required
in Active Support EventedFileUpdateChecker.

```
1) Error:
EventedFileUpdateCheckerTest#test_should_not_execute_the_block_if_no_paths_are_given:
NameError: uninitialized constant EventedFileUpdateCheckerTest::Listen
    test/evented_file_update_checker_test.rb:21:in `teardown'
```

The test was was in here twice so we were seeing this error:

```
activesupport/test/caching_test.rb:658:
warning: method redefined; discarding old test_local_cache_of_read_nil
activesupport/test/caching_test.rb:634:
warning: previous definition of test_local_cache_of_read_nil was here
```