PDF generation in read the docs is failing

Readthedocs recently turned on pdf generation failures disabling the entire doc build. This uncovered the fact that the pdf build is failing. I turned this off in `.readthedocs.yaml`, but we should investigate why this is happening. It looks like their pdf builder can't handle our math LaTeX commands.

Start by inspecting `.readthedocs.yaml` and reproducing the Read the Docs PDF build. Investigate which math LaTeX commands cause the PDF builder to fail; done means PDF generation succeeds without disabling failure handling and the documentation build passes.

Written by the indexing model from the issue text.