Deny PRs where shfmt doesn't pass

[selfhoster1312]

Hopefully this should fail as the scripts don't pass. This is just an initial attempt i haven't checked that the CI syntax is good... Wait for it ! :)

EDIT: All is good now and it was successfully applied.

[selfhoster1312]

Ready for review

[selfhoster1312]

So with the new helpers you can do:

• just check, just pre-commit, or just lint
• make check
• ./maintenance/pre-commit-check.sh
• act

The last option, act, will setup something that's really close to a Github CI runner and run the actual tests through docker. That's the entire concept and power of act and it's great!

The first 3 options require that shfmt is already setup. It's been available since like forever in distro repositories. The second option requires act which can be setup in multiple ways including one that's as simple as nix shell -p act, as long as you already have docker/podman running.

I think that's already quite a few options and i'm happy to document them. Feedback is welcome.

[Salamandar]

Thank you @selfhoster1312 <3 For the rest of your commits I pushed the shfmt_action branch, you can open a PR yourself if you want :)