Intermittent PASS in /html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/iframe-nosrc.html

https://github.com/servo/servo/actions/runs/12586345006/job/35080349999

```
Stable unexpected results (1): 
  ▶ OK /html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/iframe-nosrc.html
  └   ▶ PASS [expected FAIL] form submission
  ````