Fix user and issues autocomplete in diff notes

What does this MR do?

This MR fixes a bug where autocompletion stopped working in diff notes on MR for users and issues context menu while using characters @ & # characters respectively.

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 #32702 (closed)