docs: update fiddles/quick-start to set contextIsolation: false (#27970)

docs/fiddles/quick-start/main.js

@@ -5,7 +5,8 @@ function createWindow () {
     width: 800,
     height: 600,
     webPreferences: {
-      nodeIntegration: true
+      nodeIntegration: true,
+      contextIsolation: false
     }
   })