Intermittent PASS in `/service-workers/service-worker/fetch-event.https.html`

https://github.com/servo/servo/actions/runs/14167621774/job/39684410571

```

Stable unexpected results (1): 
  ▶ OK /service-workers/service-worker/fetch-event.https.html
  └   ▶ PASS [expected FAIL] Service Worker falls back to network in fetch event with POST form
```