Subdirectory Support

[cadojo]

I think it might be really helpful to have an option to specify the directory of the package you want to test. In a multirepo setup, folks typically use environment variables or ARGS to manually call sub-package tests. This works great, but pre-compiles the top-level-project in every parallel job.

I want to take a look at this project later this week. If I think I can, I'll submit a PR with this change if that's alright!

[ericphanson]

you can just pass the project argument: https://github.com/julia-actions/julia-runtest/blob/53f7ca9224b98d523bd6766a556c885be96e8dd8/action.yml#L29C3-L31

A docs PR to make this clear on the README would be appreciated :)