st/adjustment: Add ::actor property

Will be used by transitions to set the timeline actor.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1299

js/ui/overviewControls.js

@@ -423,6 +423,7 @@ class ControlsManager extends St.Widget {
         let activeWorkspaceIndex = workspaceManager.get_active_workspace_index();
 
         this._workspaceAdjustment = new St.Adjustment({
+            actor: this,
             value: activeWorkspaceIndex,
             lower: 0,
             page_increment: 1,

js/ui/unlockDialog.js

@@ -485,6 +485,7 @@ var UnlockDialog = GObject.registerClass({
         this._gdmClient = new Gdm.Client();
 
         this._adjustment = new St.Adjustment({
+            actor: this,
             lower: 0,
             upper: 2,
             page_size: 1,