Fix cross-project linking in the presence of external issue trackers

Copied from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7354

What does this MR do?

Fixes uses_reference_pattern? for the particular case of having a cross-project reference

• Changelog entry added
• 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

What are the relevant issue numbers?

Closes #24002 (moved)