Fix test_dict.test_pickle()

Author: vstinner

Lib/test/test_dict.py

@@ -1832,7 +1832,7 @@ def test_pickle(self):
                 frozendict(x=1, y=2),
             ):
                 p = pickle.dumps(fd, proto)
-                self.assert_is_copy(fd, pickle.loads(p))
+                self.assertEqual(fd, pickle.loads(p))
 
 
 if __name__ == "__main__":