Find a way to catch TeX rendering issues within docs build step in the CI

[DanielKotik]

At the moment, if math (TeX) expressions in the docs contain errors that lead to invalid TeX, those errors will become visible only when after the docs are built. It would be nice to allow the CI to catch such errors before the documentations goes online.

I have already done some research, but have not found a quick or easy solution.

See also: https://docs.mathjax.org/en/latest/options/input/tex.html#tex-formaterror

[DanielKotik]

A solution might be

1. add 'sphinx.ext.imgconverter' to conf.py
2. in /docs run make latex
3. cd ./_build/latex
4. latexmk -pdf -halt-on-error

It probably becomes necessary to adjust .gitignore to ignore files such as source.aux, source.fdb_latexmk, texput.fls, output.log. Also check that only the html part of the build directory will be moved to gh pages artifact.