Intermittent FAIL in `/largest-contentful-paint/broken-image-icon.html`

Seen here: https://github.com/servo/servo/actions/runs/22708532066.
```
OK /largest-contentful-paint/broken-image-icon.html
    FAIL [expected PASS] subtest: The broken image icon should not emit an LCP entry
    assert_equals: There should be one and only one LCP entry. expected 1 but got 0
```