libsForQt5.discover: mark as broken

pkgs/desktops/plasma-5/discover.nix

···
     kxmlgui
     plasma-framework
   ];
+
+  # Incompatible with our current version of fwupd:
+  # error: 'fwupd_release_get_uri' was not declared in this scope
+  meta.broken = true;
 }