tests: Ensure the git tag version check does not run for tarball builds

Do not try to determine the latest git tag if we're not in a git
repository in the first place.

test/version.t

@@ -90,6 +90,8 @@ class TestVersion(TestCase):
         # corresponding to "compiled from git" or "compiled from tarball"
         version = out.split()
 
+        # If we are within a git repository, check the tag version
+        if os.path.exists("../.git"):
           if 2 >= len(version) > 0:
               git = version[1]
               git_expected = "({0})".format(self.slurp_git())