alt Hacker Newsno; gitea and foregjo both support actions-style CI/CD and both serve mostly GH-compatible APIs and have GH-style apps. it's not 100% compatible (forgejo is more compatible than gitea), but many of your workflows might "just work" without even renaming the .github folder.
I'm one of the project leads of Gitea and we've put a ton of work into Gitea Actions, I'd be interested in any compatibility gaps that you've run into.