Intermittent FAIL in `/shadow-dom/shadow-style-invalidation-vw-units.html`

https://github.com/servo/servo/actions/runs/16729506648/job/47354451374

```
  ▶ FAIL [expected PASS] /shadow-dom/shadow-style-invalidation-vw-units.html
  │   → /shadow-dom/shadow-style-invalidation-vw-units.html ['9ec01cffc3e2fbbf4f9feb3d44d6ad7abd514f10']
  └   → /shadow-dom/shadow-style-invalidation-vw-units-ref.html ['2fabd409a0cf46c4d261316343c494eb3a9767e2']
```