bug#52172: Fix vc-git--program-version to support Git for macOS version string

[Lars Ingebrigtsen]

Dmitry Gutov <dgutov@yandex.ru> writes:

> Looks good to me (especially with included tests). The
> trailing-dot-stripping approach, that is.

OK; I've now pushed it to Emacs 29.

> I would even suggest to try to get it into emacs-28 (given that
> apparently that functionality has been broken in macOS for a long
> time).
>
> But then again, if it's only been reported now, maybe it's not hugely
> important and Emacs 28 can live without it.

This sort of change can be somewhat ticklish, as it depends on output
from external programs, and it's hard to get full test coverage of that.
So I'd rather just put it on master.

Justin, this change was small enough to apply without assigning
copyright to the FSF, but for future patches you want to submit, it
might make sense to get the paperwork started now, so that subsequent
patches can be applied speedily. Would you be willing to sign such
paperwork?