Add a github action with check-runs

[m-kuhn]

Github actions allow to run check through CI and to give feedback with inline annotations.
See https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/about-status-checks#checks

There are already a couple of github actions, but I've not seen one integrating annotations yet.
It would be super nice if shellcheck was available with this level of integration.

Please absolutely feel free to close if this is out of scope for the main project and should be left to 3rd parties. I just thought about the idea and saw that shellcheck laready features plenty of similar cool IDE integrations already.

For new checks and feature suggestions

• shellcheck.net (i.e. the latest commit) currently gives no useful warnings about this
• I searched through https://github.com/koalaman/shellcheck/issues and didn't find anything related

[piramiday]

allow me to bump this issue and upvote it! 🚀

implementing Annotations is as easy as allowing a specific output format, and has nothing to do with Github Actions or CI.

here is an excellent example that makes yamllint work with Github Annotations, out of the box! adrienverge/yamllint#322
some docs on Github Annotations: https://help.github.com/en/actions/reference/workflow-commands-for-github-actions

[szepeviktor]

@koalaman Please consider supporting --format=gha or --format=github
Thank you.

[thomasleplus]

My concern about third-party GitHub actions is that I simply don't trust them. So I hope there's an "official" one some day. In the meantime, thanks a lot for everything this project has already done.
PS: this issue seems related to (or maybe even a duplicate of) #1492.