I dislike yaml as much as the next person, but you can always “just” write Jason JSON (lol autocorrect). Unless I’m misunderstanding your criticism?

Forgejo has their own runner: https://forgejo.org/docs/latest/admin/actions/runner-installation/

I’ve used it on my personal machine, was very easy to setup and mostly compatible with GitHub actions out-of-the-box (including things like actions/checkout@v4).