async_stub doesn't need to be awaited about pytest-mock

[nicoddemus]

Hi @AstraLuma,

Can you please replace the mocker fixture to use unittest.mock instead? That is helpful to see if the problem lies with pytest-mock or with unittest.mock itself.

async def test_demo(event_loop):
    callee = unittest.mock.AsyncMock('callee')

    event_loop.call_soon_threadsafe(callee)  # Wrong!

    await asyncio.sleep(0)

    assert callee.called == 1