WebUI: always provide event variable

This is unifying coding style and avoid wrong usages.

PR #22676.

src/webui/www/private/editwebseed.html

@@ -12,7 +12,7 @@
     <script>
         "use strict";
 
-        window.addEventListener("DOMContentLoaded", () => {
+        window.addEventListener("DOMContentLoaded", (event) => {
             window.addEventListener("keydown", (event) => {
                 switch (event.key) {
                     case "Enter":