x11: Fix managed dnd

We need to actually trigger the drop from the gdk side.

gdk/x11/gdkdnd-x11.c

@@ -2855,6 +2855,7 @@ static void
 gdk_x11_drag_context_drop_performed (GdkDragContext *context,
                                      guint32         time_)
 {
+  gdk_drag_drop (context, time_);
   drag_context_ungrab (context);
 }