Run GitHub Actions faster with cache for pipenv and docker build
Update 2021-11-29 Recently we create more PRs, notice that there are a lot of redundant steps (env setup before triggering checks, etc). Found out you can cache steps in GitHub Actions, so I did some research. Got it working and turns out I reduce at least 60% actions time for a large docker image build (since only the later RUN directives are changed more frequently). For pipenv it shaved off 1 minute 18 seconds....