Doubt in `spinner_async.py` example

Hi Luciano,

I am playing a bit with the spinner_async.py example, and I am wondering why the execution finishes normally when I comment the spinner.cancel() line in the supervisor function. I think the execution should stay in an infinite loop because I am not cancelling the coroutine and, therefore the asyncio.CancelledError exception is never raised.

async def supervisor() -> int:  # <3>
    spinner = asyncio.create_task(spin('thinking!'))  # <4>
    print(f'spinner object: {spinner}')  # <5>
    result = await slow()  # <6>
    #spinner.cancel()  # <------This is the only change <7>
    return result

I am forgetting something?, any comments to help me to understand this scenario are welcome.