Issue #18622: unittest.mock.mock_open().reset_mock would recurse infinitely.

Patch from Nicola Palumbo and Laurent De Buyst.
diff --git a/NEWS b/NEWS
index 90fdb0e..90897a2 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,6 @@
+- Issue #18622: unittest.mock.mock_open().reset_mock would recurse infinitely.
+  Patch from Nicola Palumbo and Laurent De Buyst.
+
 - Issue #23661: unittest.mock side_effects can now be exceptions again. This
   was a regression vs Python 3.4. Patch from Ignacio Rossi