Skip test failing after oslo.messaging update

The newest olso.messaging release introduces a type test that fails when
the parameter is mocked. [1]

Skip the failing test in order to unblock the gate until there is a
proper fix.

[1] I0bbf9fca0ecbe71efa87c9613ffd32eb718f2c0e
Partial-Bug: 1716119

Change-Id: I414badd42f02fd6fc99957e0c72b42c26b354517

designate/tests/unit/test_mdns/test_service.py

@@ -49,6 +49,7 @@ class MdnsServiceTest(base.BaseTestCase):
         self.mdns = mdns.Service()
         self.mdns.tg = mock.Mock(name='tg')
 
+    @unittest.skip("Fails with new oslo.messaging release")
     def test_service_name(self, mc, mn, mx):
         self.assertEqual('mdns', self.mdns.service_name)