skip the test that fails on git 2.9.2
skip the test that fails on git 2.9.2

Add a skip rule to avoid running the test that fails on git version
2.9.2. When the logic involved is rewritten using dulwich in a later
patch, the skip will be removed.

Change-Id: Id8b6f74fe4feb9bec8f47c2141abfc7d463b0e57
Signed-off-by: Doug Hellmann <0798ebecfb7bc4dfb9d0445c2fa030eb64e1fa1c@doughellmann.com>

openstack/reno