The file looks like a xml file but I am not sure I can import this format.
Therefore I have also tried to convert this to a .ttl file but without success.
Also if uploading the saved file I am not sure about the namespace URI, the one contained in the file doesn’t seem to work.
The files you linked are XML Schema files that define the structural constraints of XML resources. Omeka S does not import these. Rather, it imports RDF vocabularies, which define the classes and properties needed to describe resources. VRA does have a compatible vocabulary, but does not have an importable RDF serialization, as far as I can tell.