Create dependabot.yml

[taku333]

Summary

A mechanism has been added to automatically suggest upgrades to Official Actions and Generic Actions.

[spier]

Thanks @taku333!

I have used dependabot before but I don't know what the effect of activating package-ecosystem: "github-actions" would be.

Will this create automatic Pull Requests, once a new version of the GitHub Actions is available, or how will this work?

[spier]

I found the info that I was looking for here:
https://docs.github.com/en/code-security/dependabot/working-with-dependabot/keeping-your-actions-up-to-date-with-dependabot

So I have a rough idea of how this will work.

I say let's just try it out. :)

Thank you for your contribution @taku333!

[spier]

This has certainly worked, as some PRs were created immediately :)