'Reversible' ->active_record_migrations [ci skip]

Reversible method documentation moved from migrations.md  to active_record_migrations.md
'Revert' ->active_record_migrations [ci skip]

Revert method documentation moved from migrations.md  to active_record_migrations.md
[ci skip] Fix some typos, normalize sentence.

Follow up of #16722.

https://github.com/rails/rails/pull/16722

also normalize all instance gained methods’ sentence.
form_helpers: demonstrating there is also a collection_select method in form builder
[ci skip] Fix code snippet display in Action Mailer Basics guide.
Consistently capitalize ETag.
Consistently markup etag options.
add message to `assert` in `assert_enqueued_with`
ar/connection_pool: honor overriden rack.test in middleware

Honoring an overidden `rack.test` allows testing closed connection between
multiple requests. This is useful if you're working on database resiliency, to
ensure the connection is in the expected state from one request to another on
the same worker.
Added test for exception message for validate method

- Test case for https://github.com/rails/rails/pull/16851
Merge pull request #17022 from prathamesh-sonpatki/test-for-validate-message

Added test for exception message for validate method
Merge pull request #17005 from y-yagi/fix_aj_test_helper

add message to `assert` in `assert_enqueued_with`
Added note about updating pull requests by force push

- Added note about force pushing same branch to update a existing pull
  request instead of opening new one in contributing guide.
- [ci skip]
Fix loading fixtures in engine tests

fixture_path is a class attribute of ActiveSupport::TestCase, so
ActiveSupport::TestCase.method_defined?(:fixture_path=) would always
return false.

This should fix #4971
Merge pull request #17026 from prathamesh-sonpatki/mention-updating-pull-requests

Added note about updating pull requests by force push
Merge pull request #17029 from grk/fix-loading-fixtures-in-engine-tests

Fix loading fixtures in engine tests
[CI SKIP] Improve force push note.
Merge pull request #17032 from tgxworld/update_contributing_guide

[CI SKIP] Improve force push note.
Merge pull request #17020 from Sirupsen/ar-override-rack-test

activerecord/connection_pool: honor overidden rack.test in tests
Remove --skip-action-view option from application generator