fix(GODT-3124): Race condition in sync task waiter

Fix incorrect use of `sync.WaitGroup` use to wait on sync jobs that
fail. After calling `WaitGroup.Wait()` it is advised to call
`WaitGroup.Add` until the existing counter has reached 0.

The code has been updated with a different mechanism that achieves the
same behavior which was previously available.

internal/services/syncservice/handler.go

@@ -210,12 +210,10 @@ func (t *Handler) run(ctx context.Context,
 		stageContext.metadataFetched = syncStatus.NumSyncedMessages
 		stageContext.totalMessageCount = syncStatus.TotalMessageCount
 
-		defer stageContext.Close()
-
 		t.regulator.Sync(ctx, stageContext)
 
 		// Wait on reply
-		if err := stageContext.wait(ctx); err != nil {
+		if err := stageContext.waitAndClose(ctx); err != nil {
 			return fmt.Errorf("failed sync messages: %w", err)
 		}