[GitHub Actions] disable make check all for workshop template

[fmichonneau]

because we use the styles repository for things that are not always lessons (e.g. the workshop template), we need to adjust when make lesson-check-all gets invoked.

For workshop-based repositories, we'd want to invoke make workshop-check. When it's the template itself, we could edit the index file to populate the yaml header to check the validity of the lesson (that's what we used to do on Travis CI).

It seems that we could create a new target in the Makefile (e.g., make check) that would look at the value of the kind : key in the _config.yml and depending on whether it's workshop or lesson would invoke make workshop-check or make lesson-check-all respectively so we could have a simpler GitHub actions file.