update Rails::Railtie::Configuration and ActionDispatch::Response#respond_to? to accept include_private argument
Moved "`mod_expires` to be enabled" to new line.

- Right now the comment was not rendering properly.
  # The Expires* directives requires the Apache module
  `mod_expires` to be
  # enabled.
- After this change -
  # The Expires* directives requires the Apache module
  # `mod_expires` to be enabled.
Removing merge conflict remnants in the guides.
Document ability to run a single test.
Fix doc for singularize - `pluralized` => `singularized`
Port all remaining self.protected_instance_variables to class methods
Merge pull request #12062 from strzalek/default-protected-vars

Port all remaining self.protected_instance_variables to class methods
Note functional equivalence in reset task
Add documentation for rake db:setup task
pk should not be required for hm:t associations
make sure there are actually some categories when running the test
Fix broken link to Fixtures documentation on guides
and activerecord tests

[ci skip]
Remove not necessary AR changelog entry, fix markup [ci skip]
Stop messing up with instance variables, use protected as it was meant for
Fix typos [ci skip]
Merge pull request #12076 from dabit/master

Fix broken link to Fixtures documentation on guides and activerecord tests [ci skip]
Fix typo in generators test helpr -> helper [ci skip]
Merge pull request #12078 from prathamesh-sonpatki/typo

Fix typo in generators test helpr -> helper [ci skip]
FIX reload! within rails console --sandbox causes undefined method rollback upon exiting [https://github.com/rails/rails/issues/11834]
add missing fixtures file