bpo-40275: Use new test.support helper submodules in tests (GH-20849)

diff --git a/Lib/test/libregrtest/main.py b/Lib/test/libregrtest/main.py
index adf31cc..3f9771b 100644
--- a/Lib/test/libregrtest/main.py
+++ b/Lib/test/libregrtest/main.py
@@ -20,6 +20,7 @@
 from test.libregrtest.pgo import setup_pgo_tests
 from test.libregrtest.utils import removepy, count, format_duration, printlist
 from test import support
+from test.support import os_helper
 
 
 # bpo-38203: Maximum delay in seconds to exit Python (call Py_Finalize()).
@@ -628,7 +629,7 @@
             # to a temporary and writable directory. If it's not possible to
             # create or change the CWD, the original CWD will be used.
             # The original CWD is available from support.SAVEDCWD.
-            with support.temp_cwd(test_cwd, quiet=True):
+            with os_helper.temp_cwd(test_cwd, quiet=True):
                 # When using multiprocessing, worker processes will use test_cwd
                 # as their parent temporary directory. So when the main process
                 # exit, it removes also subdirectories of worker processes.