Integrate prettify check into ci/cd

              Looking good. I have not checked the css classes any further. The final product looks good, therefore i give my okay.

Please format with prettifier before merging ♥ - done.

_Originally posted by @langehm in https://github.com/it-at-m/muc-patternlab-vue/pull/58#pullrequestreview-2045182760_
            