Mark UpdateHeadPipelineForMergeRequestWorker as idempotent
What does this MR do?
This marks the UpdateHeadPipelineForMergeRequestWorker as idempotent, meaning we'll de-duplicate it.
From gitlab-com/gl-infra/scalability#288 (closed):
The
UpdateHeadPipelineForMergeRequestWorker
processed 238k "duplicate" jobs the past 7 days, and spent 3 hours on that. Duplicate jobs are jobs that get scheduled when there is already a job in the queue for the same worker with the same arguments.