js: Listen to notify::allocation instead of allocation-changed

ClutterActors "allocation-changed" signal was removed since it's no
longer needed now that there are no ClutterAllocationFlags anymore.

See https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1245

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1245

js/ui/lookingGlass.js

@@ -833,9 +833,9 @@ class LookingGlass extends St.BoxLayout {
         Main.uiGroup.add_actor(this);
         Main.uiGroup.set_child_below_sibling(this,
                                              Main.layoutManager.panelBox);
-        Main.layoutManager.panelBox.connect('allocation-changed',
+        Main.layoutManager.panelBox.connect('notify::allocation',
                                             this._queueResize.bind(this));
-        Main.layoutManager.keyboardBox.connect('allocation-changed',
+        Main.layoutManager.keyboardBox.connect('notify::allocation',
                                                this._queueResize.bind(this));
 
         this._objInspector = new ObjInspector(this);