Link for interacting with security reports is wrong

With https://gitlab.com/gitlab-org/gitlab-ee/issues/5151 the documentation links to /help/user/project/merge_requests/index#interacting-with-security-reports, but the link doesn't exist.

The documentation has /help/user/project/merge_requests/index#interacting-with-security-reports-ultimate instead.

We should make UI and documentation consistent.