Use ruby-next branch name so we don't need to update branch name

What does this MR do and why?

Use ruby-next branch name so we don't need to update branch name

For newer rubies.

• ruby-next branch created: https://gitlab.com/gitlab-org/gitlab/-/commits/ruby-next
• ruby-next branch protected as ruby*_*

References

This is a follow up from: !178525 (comment 2309123553)

• Update ruby-sync: !178688 (merged)
• Update .gitlab-ci.yml: This merge request

This should also resolve #498470 (closed)

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