cubicweb-skos #7384645 [rdfio] Type of an RDF resource is wrongly exported as a literal [validation pending]

When exporting an RDF resource, we get rdf:type as a literal. For example:

<rdf:type>http://www.w3.org/ns/dcat#Catalog</rdf:type>

The correct result should be:

<rdf:type rdf:resource="http://www.w3.org/ns/dcat#Catalog"/>
priorityimportant
typebug
done in0.7.1
load left0.000
closed by#81dcae4977f0 [rdfio] Fix wrong rdf:type export
patch[rdfio] Fix wrong rdf:type export [applied]