[3.13] gh-124245: Fix UserWarning in test_argparse (GH-124246) (#124255)

gh-124245: Fix UserWarning in test_argparse (GH-124246)
(cherry picked from commit 992e8f6)

Co-authored-by: Serhiy Storchaka <[email protected]>

Author: miss-islington

Lib/test/test_argparse.py

@@ -5874,9 +5874,8 @@ def test_invalid_args(self):
         parser = ErrorRaisingArgumentParser(prog='PROG')
         parser.add_argument('--foo', nargs="*")
         parser.add_argument('foo')
-        with captured_stderr() as stderr:
+        with self.assertWarns(UserWarning):
             parser.parse_intermixed_args(['hello', '--foo'])
-            self.assertIn("UserWarning", stderr.getvalue())
 
 class TestIntermixedMessageContentError(TestCase):
     # case where Intermixed gives different error message