fix: [stix import] Handling potential key errors with test mechanism types
fix: [stix import] Handling potential key errors with test mechanism types

MISP/MISP,SteveClement/MISP,MISP/MISP,MISP/MISP,MISP/MISP,SteveClement/MISP,SteveClement/MISP,SteveClement/MISP,MISP/MISP,SteveClement/MISP