Convert `test_sparql/test_tsvresults.py` to pytest
Convert `test_sparql/test_tsvresults.py` to pytest

Converting to pytest in preperation for additional tests I will add for:
- https://github.com/RDFLib/rdflib/issues/1477

RDFLib/rdflib,RDFLib/rdflib,RDFLib/rdflib,RDFLib/rdflib