IMO: Also to consider is the following when switching to a new CI:

• You actually would like to drive the whole Pipeline by code (ideally typed) not YAML.
  Several methods to achieve that, certain providers are able to do dynamic pipelines (which might take slight overhead, dep. on how fast the jobs are and the pipeline generation).
  This gives some much better observability/maintainability in the long term etc. (In our projects we only do that, with Gitlab and only Nix, and with Go)
  Maybe even simplesr for nixpkgs, a tool which just generates a bunch of derivations to build which are the CI jobs, (could be anything, linting, testing, formatting etc... )?