Fix root groups redirecting to group owner

What does this MR do?

Fixes an issue where group paths at the root namespace (e.g. https://gitlab.com/mariadb-corporation) are redirected to the group owner (e.g. https://gitlab.com/ajdonnison).

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Fixes #32474