Fix missing ` in users.md

What does this MR do?

Fix missing ` in users.md

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

This is already applied in EE. Found in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6644

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Conforms to the code review guidelines
  • Has been reviewed by a Documentation specialist

What are the relevant issue numbers?

Found in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6644