Resolve "Failure in spec/migrations/fix_wrongly_renamed_routes_spec.rb"

What does this MR do?

Add the :migration metadata, and don't use factories in FixWronglyRenamedRoutes spec.

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

These migrations failures are a mess to debug/fix! :)

Why was this MR needed?

Because master is broken!

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan

What are the relevant issue numbers?

Closes #4619 (closed), #4622 (closed).