Returning `()` via `future_into_py` creates empty tuple, not `None`

[kylebarron]

Found in developmentseed/obstore#240 and with a small repro here

#[pyfunction]
pub(crate) fn return_none_async(py: Python) -> PyResult<Bound<PyAny>> {
    pyo3_async_runtimes::tokio::future_into_py(py, async move { Ok(()) })
}

This is in contrast to normal pyo3 where returning () from Rust creates a Python None.

Using pyo3 0.23 and pyo3-async-runtimes 0.23.

[davidhewitt]

Hmm, interesting. This is related maybe to PyO3/pyo3#4896