fix docs build in readthedocs

[pz-max]

pypsa-eur docs build is failing on readthedocs < see here

Changes proposed in this Pull Request

PyPSA-Earth docs are passing so I add here changes that should work on PyPSA-Eur as well:

• bump python version, see bump python version for docs built pypsa-meets-earth/pypsa-earth#717
• add setuptools, myst-parser, see parts of Documentation improvement in the configuration section_v2 pypsa-meets-earth/pypsa-earth#694

Tested these locally, and below you can also see that the readthedocs build is working

Thanks for the really cool new docs theme :)

Checklist

• I tested my contribution locally and it seems to work fine.
• A release note doc/release_notes.rst is added.

[pz-max]

Docs are passing now. Ready to merge.

[fneum]

Thanks Max! It does not seem to pass the graphviz elements:

https://pypsa-eur--658.org.readthedocs.build/en/658/tutorial_sector.html

[pz-max]

@fneum, you are right. A fix is coming 👍

[pz-max]

@fneum looks good now. Thanks INSTAGRAM https://github.com/Instagram/LibCST/pull/751/files 🥇