[flutter_tools] Update template for web application to correct typo (#48778)

packages/flutter_tools/templates/app/web/index.html.tmpl

@@ -21,7 +21,7 @@
   <script>
     if ('serviceWorker' in navigator) {
       window.addEventListener('load', function () {
-        navigator.serviceWorker.register('/service_worker.js');
+        navigator.serviceWorker.register('/flutter_service_worker.js');
       });
     }
   </script>