Support gitlab 5.x gem

What does this MR do and why?

No breaking changes appart from the drop of Ruby 2.6, 2.7 and 3.0 (end of life was 5 months ago: https://endoflife.date/ruby) support: https://github.com/NARKOZ/gitlab/releases

Minimum Ruby version supported is now 3.1 (which end of life is in 5 months: https://endoflife.date/ruby).

Screenshots or screen recordings

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How to set up and validate locally

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

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.