Issue #27531: Update signature of Mock.assert_not_called method

Since 01ae1ac2daf4, it doesn't accept any arguments.

Patch by Michael Killough.

Doc/library/unittest.mock.rst

@@ -324,7 +324,7 @@ the *new_callable* argument to :func:`patch`.
             >>> calls = [call(4), call(2), call(3)]
             >>> mock.assert_has_calls(calls, any_order=True)
 
-    .. method:: assert_not_called(*args, **kwargs)
+    .. method:: assert_not_called()
 
         Assert the mock was never called.