Use github action to auto update

[petronny]

The latest release tag of https://github.com/actions/runner can be fetched by https://developer.github.com/v3/repos/releases/#get-the-latest-release

[ioquatix]

Do you want to make a PR?

[petronny]

Maybe a few days later...

[ioquatix]

Thanks so much for working on this, I've merged your changes and I will check that it works on the next update cycle.

[petronny]

Currently we have this bug in the recent runs.

https://www.reddit.com/r/archlinux/comments/lek2ba/arch_linux_on_docker_ci_could_not_find_or_read/

I'm working on it.