Github Actions runner can be self-hosted as well! Microsoft tried to curb it for a while by making self-hosted runner minutes paid as well, but quickly walked that back.
Do note that Github Actions have been the target of like 50 different attacks and I would not combine publicly hosted code with your own runners, as without proper sandboxing it can lead to anybody executing any code on your machine just by opening a PR (might have been fixed since last I heard, but the general vibe stands).