Re-enable Trivy automatic update job

What does this MR do?

This re-enables the automatic update of Trivy scanner that was removed with !2911 (merged). Now that the blockers preventing to upgrade Trivy have been addressed we can restore this automatic update.

What are the relevant issue numbers?

gitlab-org/gitlab#435450 (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