In fairness, there's a second issue: Git repos should just support multiple hashes, so you could just add SHA-256 to a SHA-1 repo, which would then transparently support both SHAs.
This even would make the SHA-1 git objects collision resistant when stored on a trusted server, even with untrusted clients. (Exercise left to the reader.)
alt Hacker News
In fairness, there's a second issue: Git repos should just support multiple hashes, so you could just add SHA-256 to a SHA-1 repo, which would then transparently support both SHAs.
This even would make the SHA-1 git objects collision resistant when stored on a trusted server, even with untrusted clients. (Exercise left to the reader.)