Fix a code snippet typo in asyncio docs (python#108427)

Doc/library/asyncio-task.rst

@@ -592,7 +592,7 @@ Shielding From Cancellation
 
    is equivalent to::
 
-       res = await something()
+       res = await shield(something())
 
    *except* that if the coroutine containing it is cancelled, the
    Task running in ``something()`` is not cancelled.  From the point