Investigate root cause of sidekiq queueing SLI apdex drop when enabling the FF process_commit_worker_deferred

A new FF was added in gitlab-org/gitlab#553409 (closed).

Rollout tracked in https://gitlab.com/gitlab-org/gitlab/-/issues/560052.

Jerry Seto identified that enabling the FF was likely what caused the sidekiq queueing SLI breach.

This issue tracks the investigation.

This ticket was created from INC-3256 and was automatically exported by incident.io 🔥