This change makes Ladybird conform to the current requirements at
https://w3c.github.io/core-aam/#roleMappingComputedRole in the “Core
Accessibility API Mappings” spec for the case of “orphaned” li elements;
that is, any li element which doesn’t have a role=list ancestor.
The core-aam spec requires that in such cases, the li element must not
be assigned the “listitem” role but instead must be treated as if it had
no role at all.
