Add Ruby 3 builds for all GitLab libraries

This has been a bit of a moving target and we perhaps prematurely called this done in &5149 (closed)

I think we should go through the list of all GitLab-owned Ruby repositories and ensure they have a Ruby 3 build in place.

Good starting points:

• https://about.gitlab.com/handbook/engineering/projects/
• https://gitlab.com/gitlab-org/ruby/gems

We also closed gitaly-ruby in gitaly#3715 (closed) because we assumed that it would be gone by now, but it's still around. Need to either remove gitaly-ruby or add a Ruby build.

Status

• https://gitlab.com/gitlab-org/ruby/gems (there were some like https://gitlab.com/gitlab-org/ruby/gems/gitlab-puma_worker_killer that are unused, for which I did not add a build)
  • Unused: https://gitlab.com/gitlab-org/ruby/gems/gitlab-sentry-ruby (Slack)
• https://about.gitlab.com/handbook/engineering/projects/
  • gitaly-ruby - opened MR, tagged gitaly EM
  • GDK - opened MR, tagged GDK maintainers
  • gitlab-qa - opened issue
  • quality-performance - opened issue
  • gitlab-roulette
  • triage-ops - opened issue
  • customers-gitlab - opened issue
  • stopped here because I realized this is too much work; I notified folks in EWIR instead to self-review any projects they own.
• GL owned gems that don't live in https://gitlab.com/gitlab-org/ruby/gems
  • mail_smtp-pool - already done
  • sidekiq-reliable-fetcher - already done
  • gitlab-chronic_duration - fixed with MR
  • slack-notifier (the gem is called slack-messenger) - fixed with MR
  • https://gitlab.com/gitlab-org/grape-path-helpers - already done