Intermittent ERROR [expected TIMEOUT] in `/focus/focus-event-after-switching-iframes.sub.html` (WebDriver)

```
 ▶ ERROR [expected TIMEOUT] /focus/focus-event-after-switching-iframes.sub.html
  │   → No such window
```
https://github.com/servo/servo/actions/runs/19018483687/job/54309922064

https://github.com/servo/servo/actions/runs/19027680994/job/54334529106