Fix IO warning

[Zethson]

Fixes

/home/lukas/miniforge3/envs/lamindb/lib/python3.12/site-packages/anndata/utils.py:429: FutureWarning: Importing read_text from `anndata` is deprecated. Import anndata.io.read_text instead.
  warnings.warn(msg, FutureWarning)

also modernizes the setup a tiny but and removes ancient flake8 and other stuff

[Zethson]

IDK what to do about

Error: no downloadable artifacts found (expired)

[Zethson]

@LucaMarconato interested in merging this?

The RTD error is unrelated and it'll likely work with a rerun.

[Zethson]

It's been 3 months and several requested reviews. I've checked the PR again and it should not change behavior. Therefore, I'll merge it now and am ready to take any blame if I broke something.

[LucaMarconato]

Thanks!

IDK what to do about
Error: no downloadable artifacts found (expired)

To fix one had to re-run this https://github.com/scverse/spatialdata-io/actions/workflows/prepare_test_data.yaml