As part of the rewrite to the ingress networking layer/SSM for the fixed-pool-project, service executor threads that formerly yielded after sinking a message to clients no longer do so. Sys-perf performance testing revealed this to negatively impact performance for write-throughput for workloads with many change-streams listeners, and further testing showed that re-introducing the yield significantly improved write throughput on those workloads. We should add this yield back in to resolve that regression.