How do I update github actions to Node.js 20?

I got things to work by copying from other packages. My stuff in

/.github/workflows/

from SIAMFANLEquations.jl
is doing the job for me. Feel free to use my ci.yml and anything else in there.

Be aware that using other peoples’ .yml files, which I do all the time, can bite you. Take this issue, please.