5.2.1 upgrade

What does this MR do?

Upgrades Security Code Scan to 5.2.1.

This upgrade will be released as v3.0.0, which means customers will not automatically start using it, but can opt-in by overriding the SAST_ANALYZER_IMAGE_TAG for security-code-scan-sast to a value of 3.

What are the relevant issue numbers?

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