bpo-33967: Fix wrong use of assertRaises (GH-8306)

(cherry picked from commit 56d8f57b83)

Co-authored-by: INADA Naoki <methane@users.noreply.github.com>

Lib/test/test_functools.py

@@ -2192,7 +2192,7 @@ class TestSingleDispatch(unittest.TestCase):
         def f(*args):
             pass
         msg = 'f requires at least 1 positional argument'
-        with self.assertRaises(TypeError, msg=msg):
+        with self.assertRaisesRegex(TypeError, msg):
             f()
 
 if __name__ == '__main__':