GH-106214: Fix test_opcache to skip threaded tests on non-threaded platforms (GH-106166)

This skips the test added in GH-105953 on threadless builds.

Author: hoodmane

Lib/test/test_opcache.py

@@ -2,6 +2,7 @@
 import threading
 import types
 import unittest
+from test.support import threading_helper
 
 
 class TestLoadSuperAttrCache(unittest.TestCase):
@@ -484,6 +485,7 @@ def f(x, y):
             f()
 
 
+@threading_helper.requires_working_threading()
 class TestRacesDoNotCrash(unittest.TestCase):
     # Careful with these. Bigger numbers have a higher chance of catching bugs,
     # but you can also burn through a *ton* of type/dict/function versions: