bpo-34183: Fix running Lib/test/test_contextlib_async.py as a script. (GH-8381)

diff --git a/Lib/test/test_contextlib_async.py b/Lib/test/test_contextlib_async.py
index 39dcd9b..57716ae 100644
--- a/Lib/test/test_contextlib_async.py
+++ b/Lib/test/test_contextlib_async.py
@@ -4,7 +4,7 @@
 from test import support
 import unittest
 
-from .test_contextlib import TestBaseExitStack
+from test.test_contextlib import TestBaseExitStack
 
 
 def _async_test(func):