add Kafka::ProducerManager.instance.producer.close (#27807)

Author: rmtolmach

spec/lib/kafka/avro_producer_spec.rb

@@ -53,6 +53,7 @@
       end
 
       after do
+        Kafka::ProducerManager.instance.producer.close
         Singleton.__init__(Kafka::ProducerManager)
       end