adwaita-qt: add dev output

So that gtk3.dev is not included in the closure through CMake files.

pkgs/data/themes/adwaita-qt/default.nix

···
   pname = "adwaita-qt";
   version = "1.4.0";
 
+  outputs = [ "out" "dev" ];
+
   src = fetchFromGitHub {
     owner = "FedoraQt";
     repo = pname;