bpo-40275: Use new test.support helper submodules in tests (GH-21448)

diff --git a/Lib/test/test_gc.py b/Lib/test/test_gc.py
index c829708..1b096ef 100644
--- a/Lib/test/test_gc.py
+++ b/Lib/test/test_gc.py
@@ -1,8 +1,9 @@
 import unittest
 import unittest.mock
 from test.support import (verbose, refcount_test, run_unittest,
-                          cpython_only, temp_dir, TESTFN, unlink,
-                          import_module)
+                          cpython_only)
+from test.support.import_helper import import_module
+from test.support.os_helper import temp_dir, TESTFN, unlink
 from test.support.script_helper import assert_python_ok, make_script
 from test.support import threading_helper