This are some consideration about the "let's build a decentralized git solution" after the GitHub acquisition by Microsoft.
Let's start with the base: git is already decentralized. All you need is an url where other people can pull you code.
The workflow requires a way to let know other contributor about your clone and your work branch, and let them to merge it into their repos. Usually, a mailing list is used. This is the way kernel development works.
Nothing prevents you from using a federated social profile to do this (e.g, a forum profile on Friendica)
Then you need something where bug are reported. Another mailing list, another social profile? Can be.
What github/gitlab/gitea/wathever give you as a plus is a "home page" for the project where development and bug reports are easily managed and discoverable.
The downside is any of this solution require contributor to have an account there, also the self-hosted ones.
In my view, a federated replacement to git[hub,lab,ea] is not something that shout out an activity every single time a commit is inserted in the repo, but something that let me use the existing distribuited nature of git, giving me "enhanced" tools I can use with my federated identity, from my federated profile.
Ideally, I must be able to login with my federated identity (see Zot! and friendica remote auth, or OpenID) into the main instance to post bug reports, which lets me clone the repo in my instance (if supported) with a click of a button, from where I can send merge request.
Or I can just have my clone on cgit. so I must be able to initiate a merge request from the main instance. Then discussions in bug reports and merge request are federated, so I can interact with them in my timeline, If I want.