CI: Aiobotocore upgrade to 1.4 broke ci

[phofl]

The upgrade broke our ci.

Failure:
https://github.com/pandas-dev/pandas/runs/3394467341

Working:
https://github.com/pandas-dev/pandas/runs/3389494290

This comes as a dependency of s3fs, which changed the requirements already, but the 2021.08.0 release is not on conda-forge yet. We can remove the pin after it is available

https://github.com/dask/s3fs/blob/main/requirements.txt