[git-buildpackage] DEP-14 conversion: what happens if remote renamed branch upstream -> upstream/latest

[Otto Kekäläinen]

> See https://salsa.debian.org/agx/git-buildpackage/-/merge_requests/53
> and the comments there: git 2.50 handles this gracefully.

Thanks for the info! Unfortunately git 2.50 is only in unstable and
didn't make it into Trixie, so I assume most people will still
continue to run into "'refs/heads/upstream' exists; cannot create
'refs/heads/upstream/latest'