Fails to build with stricter type-argument checking of valac

[ricotz]

../src/Core/Client.vala:373.62-373.93: error: Argument 1: Cannot convert from `GLib.GenericArray<weak AppStream.Component>' to `unowned GLib.GenericArray<AppStream.Component>'
            AppStream.utils_sort_components_into_categories (appstream_pool.get_components (), category_array, true);
                                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

See https://gitlab.gnome.org/GNOME/vala/issues/696