go/worker/storage/committee: Fix worker teardown

Previously the fetch pool was closed first, which caused doneCh
to never be closed, which cause wg.Wait to never finish.

There is no need for the doneCh as fetchPool.Stop already ensures
all worker threads have stopped, and the queue of pending tasks
is emptied. In other words we are guranteed no side effects.

Author: martintomazic

.changelog/6444.bugfix.md

@@ -0,0 +1 @@
+go/worker/storage/committee: Fix worker teardown

go/worker/storage/committee/worker.go

@@ -1086,12 +1086,9 @@ func (w *Worker) Serve(ctx context.Context) error { // nolint: gocyclo
 				rootType := prevRoots[i].Type
 				if !syncing.outstanding.contains(rootType) && syncing.awaitingRetry.contains(rootType) {
 					syncing.scheduleDiff(rootType)
-					doneCh := fetchPool.Submit(func() {
+					_ = fetchPool.Submit(func() {
 						w.fetchDiff(ctx, this.Round, prevRoots[i], this.Roots[i])
 					})
-					wg.Go(func() {
-						<-doneCh
-					})
 				}
 			}
 		}