Work around Windows bug

src/python/grpcio_tests/tests/unit/_contextvars_propagation_test.py

@@ -103,7 +103,10 @@ class ContextVarsPropagationTest(unittest.TestCase):
     def test_propagation_to_auth_plugin(self):
         set_up_expected_context()
         with _server() as port:
-            target = "localhost:{}".format(port)
+            # NOTE(rbellevi): We use a literal IPV6 address because 'localhost'
+            # is not recognized as a local address by the LocalCredentials
+            # implementation on Windows.
+            target = "[::]:{}".format(port)
             local_credentials = grpc.local_channel_credentials()
             test_call_credentials = TestCallCredentials()
             call_credentials = grpc.metadata_call_credentials(