Make the gir notation for g_loadable_icon_load_finish match
the ones for g_loadable_icon_load.
https://bugzilla.gnome.org/show_bug.cgi?id=706706
* g_loadable_icon_load_finish:
* @icon: a #GLoadableIcon.
* @res: a #GAsyncResult.
- * @type: a location to store the type of the loaded icon, %NULL to ignore.
+ * @type: (out) (allow-none): a location to store the type of the
+ * loaded icon, %NULL to ignore.
* @error: a #GError location to store the error occurring, or %NULL to
* ignore.
*