[kodi] Fix lib.warn syntax for insecure package warning

Fix syntax error by wrapping permittedInsecurePackages list with
lib.warn function call. The warning now properly displays during
evaluation about qtwebengine-5.15.19 being required for
jellyfin-media-player until it migrates to qt6.

roles/kodi/default.nix

@@ -56,6 +56,12 @@ in
         firefox
       ] ++ optional cfg.appLauncherServer.enable pkgs.custom.app-launcher-server;
 
+      nixpkgs.config.permittedInsecurePackages = lib.warn
+        "Allowing insecure package qtwebengine-5.15.19 as a jellyfin-media-player dependency. Remove this once jellyfin is updated to use qt6"
+        [
+          "qtwebengine-5.15.19"
+        ];
+
       programs.kdeconnect.enable = true;
 
       systemd.user.services = mkIf cfg.appLauncherServer.enable {