fix: Remove duplicate IDs when scheduling MarkDroppedAsResolvedWorker

What does this MR do and why?

fix: Remove duplicate IDs when scheduling MarkDroppedAsResolvedWorker

Duplicate identifier IDs could previously be enqueued as we concatenate the list from the total vulnerabilities. This isn't likely to cause an issue since we stagger scheduling with a delay interval but it can be inefficient

Relates to #375128 (closed)

See kibana enqueued jobs for Vulnerabilities::MarkDroppedAsResolvedWorker worker

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.