As a Github alternative you could consider self-hosting Forgejo (https://forgejo.org/) which is the underlying system powering codeberg (mentioned earlier) and some other public instances (https://codeberg.org/forgejo-contrib/delightful-forgejo#publ...).

As a plus they provide Forgejo Actions (https://forgejo.org/docs/latest/admin/actions/) which is pretty much similar to that other Actions, and which should make migrating that much easier. (you could replace the Alpha state Forgejo runner with the Gitea forked act runner -- as they are both essentially act runner forks); or you could run any of the CI/CD tools mentioned here: https://codeberg.org/forgejo-contrib/delightful-forgejo#ci-c...