The lsst-texmf build process hasn't been updated in several years, and it's now worth making several updates to improve the stability and performance of both CI and the Docker image product going forwards:

• Switch to GitHub Actions for better performance
• Target Python 3.7 for both the test environment and the Docker image
• Use a multi-stage docker build and intermediate image caching to create a compact docker image that no longer relies on https://github.com/lsst-sqre/lsst-texlive