to fix ci errors

since annotatedRelationshipElement inherits from RelationshipElement, an
object of class annotatedRelationshipElement is obviously also instance
of RelationshipElement, therefore, it would be wrong to serialize it
twice, once as annotatedRelationshipElement and once as
RelationshipElement, Fix by checking first for relationshipElement and
then inside that check for annotatedRelationshipElement.

as they do not exist in the schema

- add "<allowDuplicates>" child with text="false" (default value), since
this attribute does not exist in the pyass implementation

- change order of the <ordered> and <value> children, to fit the order
in the schema

According to the schema, child has to exist even if it is empty

According to the schema, the child has to exist, even if it is empty

According to the xsd-schema, the child <containedElements> has to exist
even if it is empty

change location of "kind" in the serialization to the end of the asset
element

the order/sequence of the serialization of attributes was wrong.
switched the place of "derivedFrom" and "assetRef" serialization

was wrongly named JSONSerializationSchemaTest beforehand (due to
copy-paste from json test)

apparently, the schema verification does not let you add the
"schemaLocation" attribute by hand to your rootElement. Instead, the
suggested way is to use a etree.QName