Fix operating issue for scratch image

What does this MR do?

Adding metadata properties to SBOM report caused the failure of the build for scratch image where there is no operating system properties defined. This MR aims to fix this issue.

What are the relevant issue numbers?

Container scanning fails for images that do not... (gitlab-org/gitlab#428404 - closed)

Does this MR meet the acceptance criteria?

• Changelog trailer 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
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer