Ci: re-add clazy build

Clazy build on the CI was commented out as they are not passing anymore, due to 3rd party.
Apparently, one way to fix that would be to include using SYSTEM (-isystem), but I couldn't find how.

The problem has been fixed upstream too:
https://invent.kde.org/frameworks/syntax-highlighting/-/commit/04f06f6da48077de17db0da201238300fa80bbbd

See #256