Fetching: git on Mac OS (#24247)

Extend the changes in #24163 to unit tests.

var/spack/repos/builtin/packages/git/package.py

@@ -259,7 +259,8 @@ class Git(AutotoolsPackage):
     @classmethod
     def determine_version(cls, exe):
         output = Executable(exe)('--version', output=str, error=str)
-        match = re.search(r'git version (\S+)', output)
+        match = re.search(
+            spack.fetch_strategy.GitFetchStrategy.git_version_re, output)
         return match.group(1) if match else None
 
     @classmethod