Issue #13849: Fix test_null_bytes under Windows

Lib/test/test_genericpath.py

@@ -282,7 +282,7 @@ class TestGenericTest(GenericTest, unittest.TestCase):
             with self.subTest(attr=attr):
                 with self.assertRaises(ValueError) as cm:
                     getattr(self.pathmodule, attr)('/tmp\x00abcds')
-                self.assertEqual(str(cm.exception), 'embedded null byte')
+                self.assertIn('embedded null', str(cm.exception))
 
 # Following TestCase is not supposed to be run from test_genericpath.
 # It is inherited by other test modules (macpath, ntpath, posixpath).