RUF029 trigger errors on async interators

[Greesb]

Here's a sample code for reproduction:

async def test():
    return [check async for check in async_func()] 

Error:
RUF029 Function `test` is declared `async`, but doesn't `await` or use `async` features.

[charliermarsh]

Thanks!

[charliermarsh]

\cc @plredmond