Caching

[hynek]

So I've tried adding caching a few times, but it looks like the cache-dependency-path must be in the repo that runs the action.

I've went as far as resolving the action_path to an absolute path in cb01344, but that just gave me:

Error: No file in /home/runner/work/argon2-cffi/argon2-cffi matched to [/home/runner/work/_actions/hynek/build-and-inspect-python-package/v1.2/requirements/tools.txt], make sure you have checked out the target repository

And relative paths are not permitted either.

I guess I don't know enough about GitHub Actions to come up with the obvious solution, so I'll leave this open if someone comes along who does.

I guess the overarching question is, whether hashFiles can be made to hash a file in the action directory vs in the repo.

If so, we probably could cache the whole pyenv manually with https://github.com/actions/cache.

Ref #6