UX: Add title token for What's New admin page (#28476)

Followup e60b808f49,
I missed adding it here.

app/assets/javascripts/admin/addon/routes/admin-whats-new.js

@@ -1,9 +1,14 @@
 import { inject as service } from "@ember/service";
 import DiscourseRoute from "discourse/routes/discourse";
+import I18n from "discourse-i18n";
 
 export default class AdminWhatsNew extends DiscourseRoute {
   @service currentUser;
 
+  titleToken() {
+    return I18n.t("admin.dashboard.new_features.title");
+  }
+
   activate() {
     this.currentUser.set("has_unseen_features", false);
   }