This should be about impossible to enforce? Every developer and everyone who has ever cloned the repo has the complete source tree with commits. I can think of a list of countries where United States laws are not a concern, I imagine that shortly this will be one of the most distributed repositories ever.
It also shows again that while free services like Github are convenient, and truthfully their interface is the one to beat, it is better to use them as a mirror of something you self host then the primary.
Some options: (I prefer gitea - easiest to install and maintain, very active development community, single binary, written in Go)