set_actions
Description:
Sets the actions on the `GtkDragSource`.
During a DND operation, the actions are offered to potential drop targets. If actions include 
        gdk_action_move, you need to listen to the [signal@Gtk.DragSource:GtkDragSource:drag-end] signal and handle 
        delete_data being true.
This function can be called before a drag is started, or in a handler for the [signal@Gtk.DragSource:GtkDragSource:prepare] 
      signal.
Parameters:
| this | a `GtkDragSource` | 
| actions | the actions to offer |