Fix hard-deleting users when they have authored issues

What does this MR do?

Fix the "hard-delete" functionality available to administrators

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

Why was this MR needed?

If a user had authored any issues, then hard deletion broke due to a stray dependent: :restrict_with_exception invocation in the user model.

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
  • 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?

Closes #33215 (closed)