git is a distributed protocol that does not demand distribution happen through github.com

Private keys and private endpoints is all we need

There's also something like radicle: https://radicle.dev/

>Radicle is an open source, peer-to-peer code collaboration stack built on Git. Unlike centralized code hosting platforms, there is no single entity controlling the network. Repositories are replicated across peers in a decentralized manner, and users are in full control of their data and workflow.