Mathjax CDN for user guide needs to be updated again
Version 4 (of something) now generates MathJax v3, which requires us to update our CDN to something like
https://cdn.jsdelivr.net/npm/mathjax@2/MathJax.js?config=TeX-AMS-MML_HTMLorMML
See: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.mathjax