Skip the service worker for Electron

At the moment, there's no point in installing the empty service worker on
Electron.

Fixes https://github.com/vector-im/element-web/issues/16008

src/vector/index.ts

@@ -30,7 +30,7 @@ import {parseQsFromFragment} from "./url_utils";
 import './modernizr';
 
 // load service worker if available on this platform
-if ('serviceWorker' in navigator) {
+if (!window.electron && 'serviceWorker' in navigator) {
     navigator.serviceWorker.register('sw.js');
 }