Use GitHub Actions to build pdfs

[FranklinChen]

I'm currently having problems building the pdfs with make all, as LaTeX is going into an infinite loop. (This was not the case several days ago.) So it would probably be a good idea to use GitHub Actions to test building the pdfs and ensure a reproducible build.

[oetiker]

the new stuff only works if you have a current texlive (2022) installed ... but yes github actions is a good idea ... will look into it

[FranklinChen]

I do have texlive 2022 installed.

It turns out I wasn't patient enough. The build took a very long time and I initially misinterpreted some output as indicating an infinite loop of failure but I was wrong. The build works.

[marcin-serwin]

The first build is now slow because some examples are standalone PDFs, so LaTeX is started several times to produce them. These PDFs are cached so subsequent builds should be much faster.