Intermittent results in `/sanitizer-api/sanitizer-inert-document.html`

```
▶ OK /sanitizer-api/sanitizer-inert-document.html
  │   ▶ PASS [expected FAIL] Test whether setHTML loads the image.
  │   │ FAIL [expected PASS] Test whether setHTMLUnsafe loads the image.
  └   └   → promise_test: Unhandled rejection with value: "The server observed a request. It shouldn't have."
```

https://github.com/servo/servo/actions/runs/26708803654/job/78715549416