Use os_helper to fix ImportError in Python 3.10

Author: tirkarthi

tests/py39compat.py

@@ -1,4 +1,4 @@
 try:
-    from test.support.os_helpers import FS_NONASCII
+    from test.support.os_helper import FS_NONASCII
 except ImportError:
     from test.support import FS_NONASCII  # noqa