GitHub Actions feels like it was first designed to let people customize the GitHub Pages deploy flow (since GitHub by default only offered Jekyll as a static site generator, and Jekyll is Ruby tooling and not lightweight to run at all) and as a CI tool second, being molded into behaving like one after Travis CI went bad for open source projects.
Gitlab CI actually seems like it was made for CI in the first place.
I'm pretty sure of the same, and that feature actually leaks into the implementation. Right after the initial introduction of the current Github Actions, we translated some Azure Devops scripts to Actions and a lot of the structure and most keywords where nearly identical. As well as the interface when running the CI.
Gitlab CI actually seems like it was made for CI in the first place.