[#1227] morph/event: Release ants.Pool on listener stopping

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

pkg/morph/event/listener.go

@@ -621,6 +621,7 @@ func (l *listener) RegisterNotaryHandler(hi NotaryHandlerInfo) {
 func (l *listener) Stop() {
 	l.stopOnce.Do(func() {
 		l.subscriber.Close()
+		l.pool.Release()
 	})
 	l.wg.Wait()
 }