TypeError Regexp#match?(nil) in Ruby Head

It is not intended to be limited to only Rails 3 and 4, and currently runs specs against Rails 4.2 to to 5.2: https://github.com/barsoom/traco/blob/master/.travis.yml

Rubocop wants double quoted strings, not single. I missed this when I
merged #37601

Reestablish connection to previous database after migrating:

Merge pull request #37608 from bogdanvlviv/fix-assertions-for-mail-with-legacy-parameterized-delivery-job

Fix ActionMailer assertions don't work for parameterized mail with legacy delivery job

Correctly deprecate where.not working as NOR for relations:

Add String#truncate_bytes and Hash#deep_transform_values/!. Clarify Enumerable#index_with.

Allow CTEs in read-only query with postgresql

Update Welcome Aboard text in Guides [ci skip]

Update `rails server` terminal output in Guides [ci skip]

Refactor `association.scoping` not to rely on `klass.all`

Avoid LazilyDefinedAttributes being included multiple times in class, and remove methods after first use

Fix Railties test suite for Sprockets 4.0

Fix new instance creation on association relation to respect unscope

activerecord: fix some test failers caused by recent backports

Since 8297f8a3, a test fails for 6-0-stable, fixed here. In master this
is not necessary because this whole ignoring has been removed.

Fixes some warning caused by the recent minitest upgrade backport.
The fixed code doesn't exist anymore in master, so it was missed.

Enumerator should be supported by ActiveSupport::SafeBuffer

Fixed performance regression introduced MySQL 8.0

test: fix tests after minitest upgrade

Fixes fallout from e01bf7f8. One `must_be_like` was missed.

Fix an issue with duplicate preloaded records

Address to the warning "DEPRECATED: global use of assertion methods"

Follow up of #37434.

Fix eager load for no :has_many with limit and joins for :has_many

Fix autosave validation context regression