tests: replace asyncio.timeout(0) with await + suppress(CancelledError)

asyncio.timeout is 3.11+. After task.cancel(), awaiting the task raises
CancelledError once cancellation propagates; suppressing it is equivalent
to the previous TimeoutError-via-timeout(0) idiom and works on 3.10.

Author: roznawsk

tests/agent/test_agent.py

@@ -54,9 +54,8 @@ def _(notification: AllowedNotification):
     yield notifier
 
     task.cancel()
-    with suppress(asyncio.TimeoutError):
-        async with asyncio.timeout(0):
-            await task
+    with suppress(asyncio.CancelledError):
+        await task
 
 
 class TestAgentApi: