GitLab is used only for code review, issue tracking and project management. Canonical locations for source code are still https://gitweb.torproject.org/ https://git.torproject.org/ and git-rw.torproject.org.
The fallback directory code won't be exercised in the 0.2.8 alpha series unless we add some default fallback directories.
I'm just fine-tuning the list now.
See #17158 (moved) for the fallback opt-in process, and #17920 (moved) for the 0.2.8.1-alpha release.