fix: add box shadow to cookie popup

Fixes that the cookie popup didn't have a box shadow.

Fixes #29958.

Author: crisbeto

material.angular.io/src/app/shared/cookie-popup/cookie-popup.scss

@@ -4,7 +4,7 @@
 $_inner-spacing: 16px;
 
 .popup {
-  box-shadow: var(--mat-app-elevation-shadow-level-2);
+  box-shadow: var(--mat-sys-level2);
   color: var(--mat-sys-on-surface);
   background: var(--mat-sys-surface);
   position: fixed;