Gtk.Assistant.prototype.set_page_complete
function set_page_complete(page:Gtk.Widget, complete:Boolean):void {
    // Gjs wrapper for gtk_assistant_set_page_complete()
}Sets whether page contents are complete.
This will make assistant update the buttons state to be able to continue the task.
Since 2.10
- page
- a page of assistant 
- complete
- the completeness status of the page