Fix where sarif output is invalid missing cwe or shortdescription

What does this MR do?

Fixes an unlikely case where the CWE-XXX tag is missing the title text as well as a shortDescription metadata field. (Validation of this is done on downstream rules)

Bug was identified when updating semgrep rules to use the new shortDescription field: https://gitlab.com/gitlab-org/security-products/sast-rule-testing-framework/rule-testing/-/jobs/4097499692

What are the relevant issue numbers?

N/A

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Ensure the report version matches the equivalent schema version
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer