Update deprecations sort by chronological announcement milestone

What does this MR do and why?

A tiny MVC for: gitlab-com/www-gitlab-com#12450 (closed) where we update the sorting order of https://docs.gitlab.com/ee/update/deprecations.html by changing from a reversed sort of removal_milestone to a straight sort of announcement_milestone.

Screenshots or screen recordings

N/A

How to set up and validate locally

N/A

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.

Related to #12450 (closed)