Workaround use-after-free from *__fail_for_subparser tests for the moment

Author: hartwork

Lib/test/test_pyexpat.py

@@ -909,6 +909,9 @@ def test_set_activation_threshold__fail_for_subparser(self):
         subparser = parser.ExternalEntityParserCreate(None)
         setter = functools.partial(self.set_activation_threshold, subparser)
         self.assert_root_parser_failure(setter, 12345)
+        del setter
+        del subparser
+        del parser
 
     @abc.abstractmethod
     def test_set_maximum_amplification__amplification_exceeded(self):
@@ -943,6 +946,9 @@ def test_set_maximum_amplification__fail_for_subparser(self):
         subparser = parser.ExternalEntityParserCreate(None)
         setter = functools.partial(self.set_maximum_amplification, subparser)
         self.assert_root_parser_failure(setter, 123.45)
+        del setter
+        del subparser
+        del parser
 
 
 @unittest.skipIf(expat.version_info < (2, 7, 2), "requires Expat >= 2.7.2")