Fix a potential variable misuse bug (#1494)

Author: LostBenjamin

Src/StdLib/Lib/test/test_functools.py

@@ -1195,7 +1195,7 @@ class D(c.defaultdict):
         c.MutableSequence.register(D)
         bases = [c.MutableSequence, c.MutableMapping]
         for haystack in permutations(bases):
-            m = mro(D, bases)
+            m = mro(D, haystack)
             self.assertEqual(m, [D, c.MutableSequence, c.Sequence,
                                  c.defaultdict, dict, c.MutableMapping,
                                  c.Mapping, c.Sized, c.Iterable, c.Container,