administration: fix MissingCategoryDocumentConstraint with acquisition
MissingCategoryDocumentConstraint was incorrectly using unrestrictedTraverse, unlike category API which uses its own resolveCategory method with better semantics.
Because of this, some problems were not reported:
- categories using paths that resolve by acquisition, but does not exists as such (like in the test)
- categories using path with dynamic objects, like a website language.