tests: Change from expectedFailure to skip

Python 3.10 recognises unexpected passes as failures now.

Signed-off-by: Stephen Finucane <stephen@that.guru>
(cherry picked from commit 40133ec)
(cherry picked from commit 04b7b67)

patchwork/tests/test_series.py

@@ -175,7 +175,7 @@ def test_out_of_order(self):
         self.assertSerialized(patches, [2])
         self.assertSerialized(covers, [1])
 
-    @unittest.expectedFailure
+    @unittest.skip('Flaky test')
     def test_duplicated(self):
         """Series received on multiple mailing lists.