Yeah, but they also use the Pipeline features to build and deploy changes.
(They start to ruin that, but lets say, the idea is still visible.)
Granted, those build instance pull from the central git repo, and are triggered from GitLab... so also, no.
And they also said they were going to remove that ability too. Tbf to them after the inevitable response they did say they will come up with a proper solution, though that was some time ago.
Obviously the real solution is to use Bazel and not to use Gitlab CI as a crap build system.
I spent a good few months learning it and it's not the tool I would reach for in almost any circumstance unfortunately.
Docs are also lacking, which is certainly not a problem with GitlabCI
It would be nice if it had better integration with existing package managers like pip, cargo, npm and so on though. Vendoring your dependencies is fine for a big project like Chrome or Android or your company monorepo; it's a bit annoying for a small CLI tool or whatever.
Another option is something like Landlock Make, but I haven't tried it.