[gnome-shell] screenShield: Stop using deprecated actor property

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 92e5713e29ef925bfd1e3da39ced3a7e0a573192
Author: Florian Müllner <fmuellner gnome org>
Date:   Fri Sep 20 13:14:40 2019 +0200

    screenShield: Stop using deprecated actor property
    
    Both LoginDialog and UnlockDialog are now actor subclasses, so stop
    using the deprecated actor delegate that will trigger a warning.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/736

 js/ui/screenShield.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/js/ui/screenShield.js b/js/ui/screenShield.js
index f79be611c6..2e2e95a387 100644
--- a/js/ui/screenShield.js
+++ b/js/ui/screenShield.js
@@ -916,8 +916,8 @@ var ScreenShield = class {
         this._lockScreenGroup.hide();
 
         if (this._dialog) {
-            this._dialog.actor.grab_key_focus();
-            this._dialog.actor.navigate_focus(null, St.DirectionType.TAB_FORWARD, false);
+            this._dialog.grab_key_focus();
+            this._dialog.navigate_focus(null, St.DirectionType.TAB_FORWARD, false);
         }
     }