Fix error in comment for pubsub stream binder sample (spring-attic#2160)

Nit: fix an error in the comment for `inputChannel`.

Author: anguillanneuf

spring-cloud-gcp-samples/spring-cloud-gcp-pubsub-binder-sample/src/main/java/com/example/SinkExample.java

@@ -46,8 +46,9 @@ public void handleMessage(UserMessage userMessage) {
 				" at " + userMessage.getCreatedAt());
 	}
 
-	// Note that the error inputChannel is formatted as [Pub/Sub subscription name with group].[group name].errors
-	// If you change the topic name in application.properties, you also have to change the inputChannel below.
+	// Note that the error `inputChannel` is formatted as [Pub/Sub subscription name].errors
+	// or the equivalent of [Pub/Sub topic name].[group name].errors. If you change the topic name in
+	// `application.properties`, you will also have to change the `inputChannel` below.
 	@ServiceActivator(inputChannel = "my-topic.my-group.errors")
 	public void error(Message<MessagingException> message) {
 		LOGGER.error("The message that was sent is now processed by the error handler.");