Run some checks via GHA

[indigoxela]

This module has no automated tests, but phpcs and possibly jshint are good candidates to run on PRs.

[indigoxela]

Nice! It works.

But 72 errors with jshint. Hm, better fix them in a follow-up.

[indigoxela]

Just realized, there's an unused var in code-checks.yml, or more precisely, an obsolete step.

And when I'm at it - workflow and job with the same name look odd.

... And when I'm at it - check if newer phpcs version (new maintainership!!) are available via shivammathur/setup-php@v2 😉