TestRequest have been overrriding request_method setter since 2009,
but the actual implementation in Request (not TestRequest) has been
changed since that. Now it's also using @request_method instance
variable to keep the state.

The override in TestRequest have not been calling `super`, which caused
a bug that after accessing #requst_method the value was memoized and
then we've never been able to change it anymore:

```
req = ActionDispatch::TestRequest.create
puts "was: #{req.request_method}" # memoized here
req.request_method = "POST"
puts "became: #{req.request_method}"
```

output:

```
was: GET
became: GET
```

Since the whole purpose of overriding the setter in TestRequest is to
upcase it, I'm changing it to `super(method.to_s.upcase)`

Pass `set_inverse_instance` block to `sc.execute` for `SingularAssociation`

Fix table name typos [ci skip]

update doc about default `cache_store` [ci skip]

The default `cache_store` has changed in 8f0e0b63 to use `file_store`.

call `.to_h` to avoid using deprecated method

Clarify expires_now documentation 

`ActionController::Parameters#merge` call `HashWithIndifferentAccess#merge`.
In addition, it calls `HashWithIndifferentAccess#update` from
`HashWithIndifferentAccess#merge`,  where it is called the `#to_hash` of argument.
But `ActionController::Parameters#to_hash` is deprecated, warning message is
displayed.
To avoid this, modify to convert object to `Hash`.

Fixes #26415

[ci skip]

[ci skip] Simply formatting documents

Revert " [ci skip] Remove duplicate example."

 [ci skip] Remove duplicate example.

Selectively add `li ul, li ol { margin:0 1.5em; }` to subColl as needed

Remove the word "mongrel" from documents [ci skip]

Currently mongrel is not maintained.
And it couldn't be built with any Ruby versions that
supported by Rails.

It is reasonable to remove the word "mongrel" in order to avoid
confusion from newcomer.

Fix Remaining Case-In-Assignment Statement Formatting

Minor grammar fix in engines.md [ci skip]

Recently, the Rails team made an effort to keep the source code consistent, using Ruboco
(bb1ecdcc and below). Some of the case
statements were missed.

This changes the case statements' formatting and is consistent with changes
in 810dff7c and db63406c.

Remove redundant `!loaded?` condition

Remove not used alias method

Bang methods of `AR::QueryMethods` are used only internally.
We only use `left_outer_joins!`, so we can remove this alias.

Already checked `if !find_target? || loaded?`, unnecessary `!loaded?` in
elsif condition.

Move `require "models/post"` before `require "models/comment"`

use `descendants` to get class that inherited `ActiveJob::Base`

Remove unnecessary `query_scope`

change `Class#descendants` to public API [ci skip]

`Class#descendants` has already been displayed in Rails guide,
so I think that may be displayed in doc.
http://guides.rubyonrails.org/active_support_core_extensions.html#descendants

`subclasses` get only child classes.
Therefore, if create a job common parent class as `ApplicationJob`,
inherited class does not get properly.

rename test method to avoid overriding

Remove unnecessary `count` method for collection proxy

make `fixture_file_upload` work in integration tests

Currently, `fixture_file_upload` does not work in integration test.
Because, `TestProcess` module has been include in `Session` class, but
`fixture_path` can not get from `Session` class.

Modify to include `TestProcess` in `IntegrationTest` class in order to get
correct value of `fixture_path`.

Simply use its own method because `CollectionProxy` inherits `Relation`.

Update ActiveRecord callback guide for exceptions [ci skip]

07d3d402 changed how exceptions are handled in after_commit
and after_destroy callbacks.  This commit updates the 5.0
release notes and the  ActiveRecord callback guide to reflect
the new behavior.

[ci skip]