Resolve issue with showing Pipeline Occurrences without scanner

What does this MR do?

Related to #221074 (closed)

This MR introduces fix to problem with showing occurrences from security reports in Pipeline -> Security tab. The problem was caused by NoMethodError on to_hash method on report.occurrence.scanner. That rare situation happens when scanner field is missing from report occurrence (this is required field in Security Report JSON Schema). This small change will prevent us from having NoMethodError exception and will result in having empty scanner properties returned in /api/v4/projects/:project_id/vulnerability_findings API.

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After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team