aria-required-children should never fail if aria-busy=true is set

The following shouldn't fail. This bug was introduced with a change in 4.9.0, where we updated how the remediation message of aria-busy is created.

```html
<div aria-busy="true" role="tablist">
  <div role="tabpanel">
    <a href="#" role="tab">Fizzbuzz</a>
  </div>
</div>
```