Bugfix readthedocs

[Eric-Nitschke]

Minor changes:

• fix readthedocs by explicitly defining a config file in .readthedocs.yaml

Closes #1291 .

Changes proposed in this Pull Request

Minor changes:

• fix readthedocs by explicitely providing Sphinx config file in .readthedocs.yaml

Checklist

• I consent to the release of this PR's code under the AGPLv3 license and non-code contributions under CC0-1.0 and CC-BY-4.0.
• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• Newly introduced dependencies are added to envs/environment.yaml and doc/requirements.txt.
• Changes in configuration options are added in all of config.default.yaml and config.tutorial.yaml.
• Add a test config or line additions to test/ (note tests are changing the config.tutorial.yaml)
• Changes in configuration options are also documented in doc/configtables/*.csv and line references are adjusted in doc/configuration.rst and doc/tutorial.rst.
• A note for the release notes doc/release_notes.rst is amended in the format of previous release notes, including reference to the requested PR.

[Eric-Nitschke]

I am not fully proficient with readthedocs, so I welcome any advice regarding this fix.

[Eric-Nitschke]

I have no idea, why prepare_port failed on MacOS. I don't think I've changed anything that should affect the runs. It seems like it didn't manage to download the port data:

Traceback (most recent call last):
  File "/Users/runner/work/pypsa-earth/pypsa-earth/.snakemake/scripts/tmp8ud_jlhi.prepare_ports.py", line 91, in <module>
    df = download_ports().copy()
  File "/Users/runner/work/pypsa-earth/pypsa-earth/.snakemake/scripts/tmp8ud_jlhi.prepare_ports.py", line 35, in download_ports
    wpi_csv = pd.read_csv(fn, index_col=0)
    
  [...]
  
  urllib.error.URLError: <urlopen error [Errno 8] nodename nor servname provided, or not known>

I think this is odd, since the filename fn is hardcoded right above and the download shouldn't be affected by anything really.
Manually downloading the file from fn worked without issues.

[davide-f]

Many thanks @Eric-Nitschke :D
No comments and it fixes the issues!
Merging, congratulations!

[ekatef]

@Eric-Nitschke congratulations with the contribution merged, and many thanks for the fix! 🎉 🎉 🎉

Thanks for investigating the reason of CI failing! I confirm that it's quite a usual reason of CI troubles when some url is not available. In this case, re-running the test often helps 🙂 (though, agree that this issue doesn't relate to this PR at all)