Update to use "SecurityCodeScan.VS2019" package instead of deprecated package. (Fixes gitlab-org/gitlab#364736)

What does this MR do?

Currently analyzer uses deprecated SecurityCodeScan NuGet package, which produces numerous warnings in the job log output:

CSC : warning SCS9999: This package is legacy and is no longer maintained.

Minor code change to use updated SecurityCodeScan.VS2019 NuGet package which is not deprecated and no longer issues the warning.

This cleans up the job log output by removing so many unnecessary warnings.

What are the relevant issue numbers?

gitlab-org/gitlab#364736 (closed)

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

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