rack update for gitlab-backup-cli's Gemfile.next.lock

What does this MR do and why?

As described in this issue we're still seeing rack-2.2.9 bundled with the latest nightly RPMs. I suspect that the issue is that Gemfile.next.lock in gems/gitlab-backup-cli was not updated with the previous MR

Note that there appear to be a number of other Gemfile.lock updates missing from Gemfile.next.lock in gems/gitlab-backup-cli, but this MR does not attempt to fix them.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.