git: Recognize "vX.Y.GIT" versions

When Git isn't able to detect the version in its build scripts, it will fall back to use a static version string which is chosen by the maintainers. This is either the current version (v2.22.0) for a stable release, a release candidate version (v2.22.0-rc0) or a version indicating that there's been additional patches without any release candidate yet (v2.22.GIT). While we correctly parse the former two variants, the last variant we currently fail to parse.

Recognize the GIT suffix to fix building against master.