Current version of vale-action doesn't run on self-hosted runners

[dcousineau-godaddy]

So we've been hitting issues with #108 but are unable to update our vale action because we use self-hosted runners as per company policy. The problem is the action now assumes Ruby is available, which is a truthful statement when we talk specifically about GitHub provided runners (e.g. ubuntu-latest). But unfortunately cannot be assumed about self-hosted runners, and in our case the vale-action fails to run because the command gem cannot be found.

I am working with internal stakeholders to see about updating our base runner images to more closely match the environment provided by GitHub provided runners in parallel but I wanted to raise this issue to consider ways to update this action to account for these possible scenarios.

When updating, I attempted to use the ruby/setup-ruby action right before running the vale-action, however because the gem install command is run as a part of the "pre" lifecycle it appears the gem install command executes BEFORE any other Job action executes, so there's no way to manually ensure ruby is present. It's possible the commands that execute in pre.ts should move to main.ts instead so consumers can potentially ensure Ruby (or even Python) is present manually if necessary.

Alternatively vale-action could theoretically become a composite action and compose setup-ruby and setup-python to ensure dependencies are met?

I'm unsure which way is the right way and if I have time I'll look at making a contribution :)