Fix Route validation when conflicting permanent redirects exist

What does this MR do?

Prevents Route validation from failing due to descendants that have permanent redirects.

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

Why was this MR needed?

Users are being blocked from editing anything on a Group if a subgroup was renamed. https://gitlab.com/gitlab-com/support-forum/issues/2883

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-com/support-forum/issues/2883 Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/41786