Testdir.finalize: skip monkeypatch.undo()

This gets done via the fixture itself.
Ref: pytest-dev#6219 (comment)

Author: blueyed

src/_pytest/pytester.py

@@ -593,7 +593,6 @@ def finalize(self):
         self._sys_modules_snapshot.restore()
         self._sys_path_snapshot.restore()
         self._cwd_snapshot.restore()
-        self.monkeypatch.undo()
 
     def __take_sys_modules_snapshot(self):
         # some zope modules used by twisted-related tests keep internal state