gh-134309: Add ``github.actor`` to the GitHub Actions concurrency key (#134310)

When inexperienced users create a PR from their default branch, all of the concurrency keys
collide as there is no namespacing. This becomes an issue at events with many new contributors,
where workflow runs are cancelled on other pull requests.
Disambiguate by adding the username of the relevant 'actor' to the concurrency key.

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
Co-authored-by: Sviatoslav Sydorenko <sviat@redhat.com>
Co-authored-by: C.A.M. Gerlach <CAM.Gerlach@Gerlach.CAM>
Authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>