Fix test_worker_waits_for_scheduler (#6155)
Fix test_worker_waits_for_scheduler (#6155)

Remove asyncio.wait_for from test.
It seems to be malfunctioning very rarely.
We replace it with a less sophisticated task + sleep + cancel.

Fixes https://github.com/dask/distributed/issues/6153
dask/distributed,dask/distributed,dask/distributed,dask/distributed