Bump Gitlab Shell version to 13.23.2

What does this MR do and why?

v13.23.2

• Bump labkit version to 1.12.0 gitlab-shell!569 (merged)
• Add title and correct copyright notice to license gitlab-shell!568 (merged)
• Bump go-proxyproto package gitlab-shell!563 (merged)
• Update Go to version 1.17.6 gitlab-shell!562 (merged)

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Unblocks https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/15189#note_839165905