Change gui_dialog_add_widget() to not use gui_container_add() that is going away in gtk-3.98.4. While at it, rename gui_dialog_add_widget() as gui_dialog_add_action_widget() to better distinguish it from gui_dialog_add_content_widget(). Replace direct gui_container_add(gui_dialog->action_area) calls with gui_dialog_add_action_widget().
Change gui_dialog_add_widget() to not use gui_container_add() that is going away in gtk-3.98.4. While at it, rename gui_dialog_add_widget() as gui_dialog_add_action_widget() to better distinguish it from gui_dialog_add_content_widget(). Replace direct gui_container_add(gui_dialog->action_area) calls with gui_dialog_add_action_widget().