This is how we did things with Jenkins and gitlab runners before, idk why folks would do it differently for GHA.

If you can't run the same scripts locally (minus external hosted service/API) then how do you debug them w/o running the whole pipeline?

I assume you're using the currently recommended docker-in-docker method. The legacy Gitlab way is horrible and it makes it basically impossible to run pipelines locally.

GitHub introduced all their fancy GHA apps or callables or whatever they're called for specific tasks, and the community went wild. Then people built test and build workflows entirely in GHA instead of independent of it. And added tons of complexity to the point they have a whole build and test application written in GHA YAML.