Prevent cancellation of task with timeout in asyncio runner.

I am yet unclear why on new python/os/websocket we do not get
a timeout error, however from what I could tell, wait_for would
cancel the websocket.recv and that stops instead of throwing
a timeout exception, resulting in a full success result.

Making this change seems to make the test TestPurposefulFailureExtraReportingOnToggle
pass on my machine (well ... fail as expected instead of passing with a
successful stop)

scripts/py_matter_yamltests/matter_yamltests/runner.py

@@ -162,7 +162,8 @@ async def _run_with_timeout(self, parser: TestParser, config: TestRunnerConfig):
         try:
             if config.auto_start_stop:
                 await self.start()
-            status = await asyncio.wait_for(self._run(parser, config), parser.timeout)
+            task = self._run(parser, config)
+            status = await asyncio.wait_for(asyncio.shield(task), parser.timeout)
         except (Exception, CancelledError) as exception:
             status = exception
         finally: