fix: [stix export] Bump minimum CybOX version to 2.1.0.21
fix: [stix export] Bump minimum CybOX version to 2.1.0.21

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