But getting the entire country's law into git is already an impressive feat.
Not git, but Congress actually does have quite a bit of data digitized. A random example[0] -they even provide XML. The Congress data is going to give you all bills - many of which do not pass, so a different mission than this project.
[0] https://www.congress.gov/bill/118th-congress/house-bill/4818
Git isn't structured for collaborative commits, but community-wide conventions kind of "patches" support for it on top of the git message body, via "Co-Authored-By: name <name@example.com>" which IIRC most platforms support, and the convention itself initially comes from Linux kernel development.