Fix flaky release_created_audit_event_service_spec

What does this MR do and why?

1. ReleaseCreatedAuditEventService uses release.milestone_titles to log the audit event which uses order_by_dates_and_title scope defined in the Milestone class.
2. Originally the test used Milestone.first and Milestone.second for assertion in the tests, however, it could be flaky sometimes because of the order by title clause.
3. This MR fixes the flakiness in the test.

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Related to #383040 (closed)