Update intersphinx_mapping for Sphinx 8 compatibility

[musicinmybrain]

This makes the intersphinx_mapping in docs/source/conf.py forward-compatible with Sphinx 8 by changing it from

intersphinx_mapping = {'https://docs.python.org/3/': None}

to

intersphinx_mapping = {'python': ('https://docs.python.org/3/', None)}