Crosslink to issues that introduced `Parallel push checks`

The following discussion from !51352 (merged) should be addressed:

• @aqualls started a discussion: (+1 comment)

  @robotmay_gitlab we are mostly ready to go! I don't have issue links or information on when these flags were 1) introduced and 2) enabled on specific projects on GitLab.com.

  Get me this info and I will HAPPILY get this merge request out the door!

  (Fixing these links will also get you a green pipeline.)