Intermittent TIMEOUT in `/content-security-policy/inheritance/document-write-iframe.html`

```
Stable unexpected results (1): 
  ▶ TIMEOUT [expected OK] /content-security-policy/inheritance/document-write-iframe.html
  │   ▶ TIMEOUT [expected PASS] document.open() keeps inherited CSPs on transient about:blank.
  └   └   → Test timed out
```
https://github.com/servo/servo/actions/runs/20124735261/job/57752272585