Fix documentation of spring.kafka.producer.batch-size

Closes gh-13127

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -917,7 +917,7 @@ content into your application; rather pick only the properties that you need.
 	spring.kafka.listener.concurrency= # Number of threads to run in the listener containers.
 	spring.kafka.listener.poll-timeout= # Timeout in milliseconds to use when polling the consumer.
 	spring.kafka.producer.acks= # Number of acknowledgments the producer requires the leader to have received before considering a request complete.
-	spring.kafka.producer.batch-size= # Number of records to batch before sending.
+	spring.kafka.producer.batch-size= # Default batch size in bytes.
 	spring.kafka.producer.bootstrap-servers= # Comma-delimited list of host:port pairs to use for establishing the initial connection to the Kafka cluster.
 	spring.kafka.producer.buffer-memory= # Total bytes of memory the producer can use to buffer records waiting to be sent to the server.
 	spring.kafka.producer.client-id= # Id to pass to the server when making requests; used for server-side logging.