Fix conflicting redirect search

What does this MR do?

Fixes query for conflicting redirects by matching case-insensitively.

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

I used LOWER instead of ILIKE because we recently added an index for searching redirects by LOWER.

Why was this MR needed?

Reproduce bug

1. Create group 'Foo'
2. Create project 'Foo/bar'
3. Rename group 'Foo' to 'baz'
4. See redirect from 'Foo/bar' to 'baz/bar'
5. Create group 'foo'
6. Redirect from 'Foo/bar' to 'baz/bar' remains, but should have been destroyed

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
• 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
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?