Use 3.9 test helper

Author: encukou

Lib/test/test_sundry.py

@@ -28,7 +28,7 @@ def test_untested_modules_can_be_imported(self):
                     print("skipping tty")
 
     def test_distutils_modules(self):
-        with warnings_helper.check_warnings(quiet=True):
+        with support.check_warnings(quiet=True):
 
             path_copy = sys.path[:]
             import distutils