Added test cases for checking redundant audit events

What does this MR do and why?

Added test cases for checking no audit events are being created when there is no change in updated values in https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/lib/audit/external_status_check_changes_auditor.rb.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.

Related to #370348 (closed)