Example failure: https://buildkite.com/rails/rails/builds/68074#0fe7ca54-fcce-4a47-85db-a784275c8f51/1115-1125

Each time a job is serialized, `enqueued_at` is updated.  Thus, separate
serializations of the same job can have different `enqueued_at`
timestamps if the serializations do not occur within the same second.