Allow group reporters to promote labels

What does this MR do?

Allow people who have access to admin group labels (group reporters and higher) to also promote project labels.

Are there points in the code the reviewer needs to double check?

Don't think so!

Why was this MR needed?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11876 changed the permissions, but promotion wasn't actually checking admin_label. @victorwu asked about this in https://gitlab.com/gitlab-org/gitlab-ce/issues/33154#note_31762070.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/33473.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together