Added arugment error when pipeline is nil

What does this MR do and why?

FindingBuilder class inside the VulnerabilityScanning module was not checking for the edge case when pipeline argument is nil for the Sbom::Occurence which was causing GlobalAdvisoryScanWorker to fail. Thus, an argument error is raised to let the AdvisoryScan job continue it's flow.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #437120 (closed)