Use gitlab-shell 13.23.0

What does this MR do and why?

This bumps the gitlab-shell version to 13.23.0. See gitlab-shell!558 (merged) for the changelog. The only non-documentation change is optional support for SSHUploadPackWithSidechannel, see gitlab-com/gl-infra&652 (closed). By default we still don't use the new RPC. Its use is controlled by the gitlab_shell_upload_pack_sidechannel feature flag added in !78668 (merged).

Closes gitlab-com/gl-infra/scalability#1514

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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