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.
Related to Onionoo ticket #25848 (moved) and metrics-lib ticket #26159 (moved), we should replace Gson with Jackson in CollecTor. For reasons, see those tickets. I'll work on this.