Fix approval notification for MRs without scan result policies

What does this MR do and why?

This MR fixes a bug in approval notification where the note was created if MR does not have scan result policy applied.

Addresses #415706 (closed)

Screenshots or screen recordings

How to set up and validate locally

• Create a project with more than 2 security scanners
• Enable security_policy_approval_notification feature flag for the project
• Create an MR that removes one of the security scanners
• Verify that the MR has a note posted by GitLab Security Bot

Example Project: https://gitlab.com/gitlab-org/govern/security-policies/sashis-test-group/without-srp Example MR: gitlab-org/govern/security-policies/sashis-test-group/without-srp!2

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.