No Bug - [mozversioncontrol] xfail 'test_branch.py' with git < 2.22.0, r=bhearsum

The 'git branch --show-current' flag didn't exist prior to that version.

Differential Revision: https://phabricator.services.mozilla.com/D112043

python/mozversioncontrol/test/test_branch.py

@@ -2,7 +2,10 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+from distutils.version import LooseVersion
+
 import mozunit
+import pytest
 
 from mozversioncontrol import get_repository_object
 
@@ -31,6 +34,9 @@ STEPS = {
 
 def test_branch(repo):
     vcs = get_repository_object(repo.strpath)
+    if vcs.name == "git" and LooseVersion(vcs.tool_version) < LooseVersion("2.22.0"):
+        pytest.xfail("`git branch --show-current` not implemented yet")
+
     if vcs.name == "git":
         assert vcs.branch == "master"
     else: