Windows doesn't have os.fork(). I'll just disable this test for now

Lib/test/test_mailbox.py

@@ -723,6 +723,8 @@ class _TestMboxMMDF(TestMailbox):
     def test_lock_conflict(self):
         # Fork off a subprocess that will lock the file for 2 seconds,
         # unlock it, and then exit.
+        if not hasattr(os, 'fork'):
+            return
         pid = os.fork()
         if pid == 0:
             # In the child, lock the mailbox.