Issues with building docs

[Alex Botev]

Since a week ago aprarently our docs are failing with the following message:
```
  File "/home/docs/checkouts/readthedocs.org/user_builds/kfac-jax/envs/latest/lib/python3.7/site-packages/jax/_src/dispatch.py", line 58, in <module> from etils import epath File "/home/docs/checkouts/readthedocs.org/user_builds/kfac-jax/envs/latest/lib/python3.7/site-packages/etils/epath/__init__.py", line 23, in <module> from etils.epath.resource_utils import resource_path File "/home/docs/checkouts/readthedocs.org/user_builds/kfac-jax/envs/latest/lib/python3.7/site-packages/etils/epath/resource_utils.py", line 34, in <module> import importlib_resources File "/home/docs/checkouts/readthedocs.org/user_builds/kfac-jax/envs/latest/lib/python3.7/site-packages/importlib_resources/__init__.py", line 3, in <module> from ._common import ( File "/home/docs/checkouts/readthedocs.org/user_builds/kfac-jax/envs/latest/lib/python3.7/site-packages/importlib_resources/_common.py", line 86, in <module> def _(cand: None) -> types.ModuleType: File "/home/docs/checkouts/readthedocs.org/user_builds/kfac-jax/envs/latest/lib/python3.7/functools.py", line 827, in register f"Invalid annotation for {argname!r}. {cls!r} is not a class." AssertionError: Invalid annotation for 'cand'. None is not a class.
```
We are using Sphinx v4.5.0. Any ideas why this is happening?