bpo-40275: Adding threading_helper submodule in test.support (GH-20263)

diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index 0db7d30..7d4376a 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -31,6 +31,7 @@
 import warnings
 from test import support
 from test.support import socket_helper
+from test.support import threading_helper
 from platform import win32_is_iot
 
 try:
@@ -3163,12 +3164,12 @@
 
     @classmethod
     def setUpClass(cls):
-        cls.key = support.threading_setup()
+        cls.key = threading_helper.threading_setup()
         create_file(support.TESTFN, cls.DATA)
 
     @classmethod
     def tearDownClass(cls):
-        support.threading_cleanup(*cls.key)
+        threading_helper.threading_cleanup(*cls.key)
         support.unlink(support.TESTFN)
 
     def setUp(self):