Readthedocs is failing on configuration error

[EwoutH]

All our recent docs builds have been failing: https://readthedocs.org/projects/mesa/builds/

• Last passing build: https://readthedocs.org/projects/mesa/builds/25212355/
• First failing build: https://readthedocs.org/projects/mesa/builds/25223548/

The error at hand, which originates in the cat docs/conf.py step:

ERROR: Invalid value `None` in intersphinx_mapping['http://docs.python.org/']. Expected a two-element tuple or list.

It looks like the error is caused by this line:

mesa/docs/conf.py

Line 282 in f00ff96

intersphinx_mapping = {"http://docs.python.org/": None}

Which hasn't been touched in 10 years.

[EwoutH]

It seems the update from Sphinx v7.4.7 to Sphinx v8.0.2 caused this issue.

[EwoutH]

Traced back the issue to this PR:

• Remove support for the Sphinx 0.5 intersphinx_mapping format sphinx-doc/sphinx#12083

Should be fixed by #2206.