Fix testpatch.PatchTest.test_exit_idempotent

.stop() and __exit__ have subtly different code paths, so to really test __exit__ idempotency, we need to call it specifically twice.

Author: cjw296

Lib/test/test_unittest/testmock/testpatch.py

@@ -748,7 +748,7 @@ def test_stop_idempotent(self):
     def test_exit_idempotent(self):
         patcher = patch(foo_name, 'bar', 3)
         with patcher:
-            patcher.stop()
+            patcher.__exit__(None, None, None)
 
 
     def test_second_start_failure(self):