Linus ranted[0] about how it's idiotic to worry about SHA-1 collisions in 2005 months after significant weaknesses[1] were found in it (which have recently been demonstrated by Google). I'm certainly not about to waste effort making a patch that he's going to reject as idiotic.

[0] http://www.gelato.unsw.edu.au/archives/git/0504/0885.html

[1] https://www.schneier.com/blog/archives/2005/02/sha1_broken.h...