Just a note - you can host your own CI node (runner) for project(s) on gitlab.com. It's super simple to setup, too.
https://docs.gitlab.com/runner/install/linux-repository.html
https://docs.gitlab.com/runner/install/linux-repository.html
Fully self-hosted looks like the only sane way. Harder to set up, but at least one can check the whole chain that way.