The architecture I propose for achieving this is treating git servers like relays. The nostr repository event includes a list of git servers and the commit-ids for the tips of each branch. a git remote-helper enables maintainers to push to all git server mirrors and update the repo event with the new branch tip with a simple 'git push' command. I wrote a bit more about the proposed repo event format for this here: https://github.com/nostr-protocol/nips/pull/997#discussion_r1464484832
Discussion
I hope you guys get the bounty ! Perhaps after some more refinement to meet the terms ?