Disable sub_group_issuables_spec.rb for mysql

Closes #33057

See merge request !11795

Make `ActiveRecord::Migrator` idempotent again in test environment

Closes #33030

See merge request !11762

Fix alignment of tree symbols in merge requests

Closes #29590

See merge request !11761

Merge branch '19107-404-when-creating-new-milestone-or-issue-for-project-that-has-issues-disabled' into 'master'

'New issue'/'New merge request' dropdowns should show only projects with issues/merge requests feature enabled

Closes #19107

See merge request !11754

Merge branch '33048-markdown-rendering-of-md-files-has-ceased-to-display-latex-equations' into 'master'

Fix math rendering on blob pages

Closes #33048

See merge request !11793

Merge branch '33032-invalid-you-directly-addressed-yourself-todo-when-using-unsubscribe' into 'master'

Resolve "Invalid 'You directly addressed yourself' TODO when using `/unsubscribe`"

Closes #33032

See merge request !11788

Fix omniauth-google-oauth2 dependencies in Gemfile.lock

Closes #32653

See merge request !11787

`renderGFM` adds the correct syntax highlighting class and triggers KaTeX if
required.

Use 'sudo bash' when adding nodesource repository

See merge request !10527

Resolve "Browser notifications for pipeline running in a MR is gone"

Closes #32916

See merge request !11734

Set head pipeline when creating merge requests

See merge request !11669

The /unsubscribe slash command means that we check if the current user is
subscribed to the issuable without having an explicit subscription. That means
that we use the UserParser to find references to them in the notes.

The UserParser (and all parsers inheriting from BaseParser) use RequestStore to
cache ActiveRecord objects, so that we don't need to load the User object each
time, if we're parsing references a bunch of times in the same request.

However, it was always returning _all_ of the previously cached items, not just
the ones matching the IDs passed. This would mean that we did two runs through
with UserParser if you were mentioned in a comment, and then mentioned someone
else in your comment while using /unsubscribe:

1. Because /unsubscribe was used, we see if you were mentioned in any comments.
2. Because you mentioned someone, we find them - but we would also get back your
   user, even if you didn't mention yourself. This would have the effect of
   creating a mention or directly addressed todo for yourself incorrectly.

The fix is simple: only return values from the cache matching the IDs passed.