Intermittent PASS in `/paint-timing/fcp-only/fcp-with-rtl.html`

```
Stable unexpected results (1)
  ▶ OK /paint-timing/fcp-only/fcp-with-rtl.html
  └   PASS [expected FAIL] subtest: FCP should fire when coordinates are negative, if within document scrollable area
```
https://github.com/shubhamg13/servo/actions/runs/21279775181