Fix broken dependency list for invalid Container Scanning pkg mgr type

What does this MR do and why?

This MR fixes a bug affecting the dependency list when Container Scanning reports are present. Container Scanning reports contain dependency_files[].package_manager fields with strings that are not properly converted into purl_type values, causing invalid NULL SQL queries, which this MR fixes.

Related issues

Dependency list page throws error if Container ... (#420664 - closed)

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.

Related to #420664 (closed)