Add +variants to ActionView::FileSystemResolver documentation.
Merge pull request #17070 from felipecvo/master

Add +variants to ActionView::FileSystemResolver documentation.
Don’t require already required modules

abstract_unit.rb requires `action_controller` which [already includes the following lines of code](https://github.com/rails/rails/blob/64fcdce1d3a6a8768ab17f3be144270456814f82/actionpack/lib/action_controller.rb#L2L3):

```ruby
require 'abstract_controller'
require 'action_dispatch'
```
Merge pull request #17071 from claudiob/don-t-require-action-dispatch-twice

Don’t require already required modules
Preparing for 4.2.0.beta2 release
Add documentation about `config.action_dispatch.rescue_responses`

[ci skip]
Merge pull request #17076 from yuki24/write-doc-for-rescue-responses

Add documentation about rescue_responses in Configuring [ci skip]
[ci skip] fix typo in set examples
Merge pull request #17079 from y-yagi/patch-1

[ci skip] fix typo in set examples
some object allocation reduction for new AR objects

Benchmark:

```ruby
require 'objspace'
require 'active_record'

ActiveRecord::Base.establish_connection adapter: "sqlite3",
                                        database: ":memory:"

ActiveRecord::Base.connection.instance_eval do
  create_table(:articles) { |t| t.string :name }
end

class Article < ActiveRecord::Base; end
a = Article.create name: "foo"
a = Article.find a.id

N = 10
ObjectSpace::AllocationTracer.trace do
  N.times { Article.find a.id }
end
ObjectSpace::AllocationTracer.allocated_count_table
table.sort_by { |_,x| x }.each do |k,v|
  p k => (v / N)
end
```
Fix typo in AR changelog

- middlware -> middleware
Merge pull request #17080 from prathamesh-sonpatki/fix-typo-in-ar-changelog

Fix typo in AR changelog [ci skip]
Fix some typos in ActiveJob

[ci skip]
Merge pull request #17081 from prathamesh-sonpatki/fix-aj-typos

Fix some typos in ActiveJob
Fix typo in upgrading guide

- [ci skip]
- behvaior -> behavior
Merge pull request #17082 from prathamesh-sonpatki/fix-typo-in-upgrading-guide

Fix typo in upgrading guide
Make AJ integration tests much less verbose

In passing, avoid a blind retry in QC: instead, just fix the problem.
Tiny follow-up to #16999 [ci skip]

* Fix a typo
* Remove references to Rails version
* Remove an extra whitespace