Closes #37595

In the getting started, we're asked to add `"<h1>New Article</h1>"`
while later on in the guide it is referenced as `"<h1>New article</h1>"`

This pull request aims at fixing this small inconsistency.

[ci skip]

Fix collection callbacks not terminating when abort is thrown

Fix the collision check for the scaffold generator

Co-authored-by: NAllen Hsu <allen.hsusp@gmail.com>

Currently `wrapped` is a String.  Instead pass Class so that Sidekiq can get access to the ActiveJob and its configuration without having to constantize.  I verified that `JobClass.to_s` == `"JobClass"` so serialization to JSON should not be affected.

```ruby
> JSON.dump({"wrapped" => SomeJob})
=> "{\"wrapped\":\"SomeJob\"}"
```

By having access to the ActiveJob class, Sidekiq can get access to any `sidekiq_options` which have been set on that ActiveJob type and serialize those options into Redis.

https://github.com/mperham/sidekiq/blob/master/Changes.md#60

Use singular, `instance`, in deprecation warning.

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