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.
https://support.torproject.org/tbb/tbb-12/ ( from https://support.torproject.org/#faq )
"and we recommend you do not enable it."
"and we recommend you to not enable it."