fix test as wait_for no longer creates

a new task so no sleep is required

Lib/test/test_asyncio/test_waitfor.py

@@ -237,8 +237,8 @@ async def inner():
         with self.assertRaises(FooException):
             await foo()
 
-    @unittest.skip("TODO")
     async def test_wait_for_self_cancellation(self):
+        loop = asyncio.get_running_loop()
         async def inner():
             try:
                 await asyncio.sleep(0.3)
@@ -257,7 +257,6 @@ async def inner():
         # Test that wait_for itself is properly cancellable
         # even when the initial task holds up the initial cancellation.
         task = asyncio.create_task(wait)
-        await asyncio.sleep(0.2)
         task.cancel()
 
         with self.assertRaises(asyncio.CancelledError):