The addons plugin no longer shows an icon in the notification area when the option is selected.
My quick diagnosis is that this is because Geany 1.23 no longer sets the icon, it sets the icon name, meaning the addons needs to use gtk_window_get_icon_name and then go and find the icon by name. (Or probably it could just know the name is "geany" and look that up :)
Cheers Lex