Follow-up from "Add warning alert for composite_identity_forbidden"

The following discussion from !205095 (merged) should be addressed:

• @GitLabDuo started a discussion: (+3 comments)

  Inconsistent access to failure_reason: Line 15 uses read_attribute(:failure_reason) while line 22 uses failure_reason. This inconsistency could lead to different behaviors if there are model-level transformations on the failure_reason attribute.

    - has_composite_identity_forbidden = @pipeline.failure_reason == 'composite_identity_forbidden'