Then it sounds like public open source projects are now illegal in the US. We should act accordingly.
Alternatively we can continue like normal because not much of value will be lost. Git is inherently decentralized. If A requires work by C they can pull it directly or B can pull from C and A from B.
There is no inherent issue with C's contributions coming in by way of B especially if B vetted and examined said contributions personally.
Please see the legal reason in the sibling comment.