Add Ruby upgrade guidelines to global navigation

What does this MR do and why?

I noticed when looking for information about Ruby version requirements that this development documentation didn't have a global navigation item.

Page was added in gitlab!68955 (merged).

CC @mkaeppler

Screenshots, screen recordings, or links to review app

• Before: https://docs.gitlab.com/ee/development/ruby_upgrade.html
• After: https://eread-add-ruby-upgrade-guidelines-to-global-navigation.docs.gitlab-review.app/ee/development/ruby_upgrade.html

Merge request acceptance checklist

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