bpo-35601: Alleviate race condition when waiting for SIGALRM in test_asyncio (GH-11337)

There is a race condition regarding signal delivery in test_signal_handling_args for
test_asyncio.test_events.KqueueEventLoopTests. The signal can be received at any moment outside the time window provided in the test. The fix is to wait for the signal to be received instead with a bigger timeout.