test_jsoning: Instead of inheriting DatamodelVisitor use _PartialDatamodelVisitor
test_jsoning: Instead of inheriting DatamodelVisitor use _PartialDatamodelVisitor

userzimmermann/robotframework-python3,userzimmermann/robotframework-python3,Senseg/robotframework,userzimmermann/robotframework-python3,Senseg/robotframework,Senseg/robotframework,Senseg/robotframework,Senseg/robotframework,userzimmermann/robotframework-python3,userzimmermann/robotframework-python3