Fix missing and duplicates on project milestone listing page

What does this MR do?

Sorts by Milestone id DESC, along with the existing ordering on project's milestone list page.

Are there points in the code the reviewer needs to double check?

This ~bug may be hidden in other places that overrides / implements sort_by_attribute, if the AR relation (caller) doesn't include a unique ID ordering in place.

Maybe we could have a follow up issue for Quality test with a more generic test for paginated collections, ensuring we have no missing or duplicates.

Why was this MR needed?

https://gitlab.com/gitlab-org/gitlab-ce/issues/37078

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/37078