Ci: re-add clazy build

[narnaud]

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