fix tests on systems that can't validate python.org

Lib/test/test_site.py

@@ -412,6 +412,7 @@ class ImportSideEffectTests(unittest.TestCase):
                 self.fail("sitecustomize not imported automatically")
 
     @test.support.requires_resource('network')
+    @test.support.system_must_validate_cert
     @unittest.skipUnless(sys.version_info[3] == 'final',
                          'only for released versions')
     @unittest.skipUnless(hasattr(urllib.request, "HTTPSHandler"),