And yet, GitHub Actions are notoriously broken, and serious customers are self-hosting their runners.

Codeberg does have some free CI runners, although I’m not sure what capacity they currently have, and how well it would work out if everybody decides to switch from GitHub today. They do encourage you to pick the smallest runner that works for you, and keep the workflows lean: https://codeberg.org/actions/meta

Or you can self-host your own runners too, of course.

Edit: there’s one caveat – Forgejo Actions are Linux only. If you need Windows or macOS runners, this won’t work for you. But... you could have a readonly GitHub mirror (which you should probably do if you want people to discover your project), and use the GitHub Actions runners for free :-)