Fix typo: equivalent code of `async with cond` (GH-11681)

Doc/library/asyncio-sync.rst

@@ -180,11 +180,11 @@ Condition
        cond = asyncio.Condition()
 
        # ... later
-       await lock.acquire()
+       await cond.acquire()
        try:
            await cond.wait()
        finally:
-           lock.release()
+           cond.release()
 
    .. coroutinemethod:: acquire()