st/viewport: Invalidate transform when it changes

Since ClutterActor now caches the whole transformation matrix for an
actor, we need to invalidate the cached transform if the matrix returned
by apply_transform() implementations changes.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1308

src/st/st-viewport.c

@@ -78,6 +78,7 @@ adjustment_value_notify_cb (StAdjustment *adjustment,
                             GParamSpec   *pspec,
                             StViewport   *viewport)
 {
+  clutter_actor_invalidate_transform (CLUTTER_ACTOR (viewport));
   clutter_actor_queue_relayout (CLUTTER_ACTOR (viewport));
 }