GI can only figure out the correct scope if there's a GDestroyNotify
or GAsyncReadyCallback parameter.
* @widget_class: a #GtkWidgetClass
* @action_name: a prefixed action name, such as "clipboard.paste"
* @parameter_type: (nullable): the parameter type, or %NULL
- * @activate: callback to use when the action is activated
+ * @activate: (scope call): callback to use when the action is activated
*
* This should be called at class initialization time to specify
* actions to be added for all instances of this class.