Reduce logging for unsent SUBSCRIBE messages

Closes gh-28252

Author: rstoyanchev

spring-websocket/src/main/java/org/springframework/web/socket/messaging/StompSubProtocolHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -366,10 +366,10 @@ else if (StompCommand.UNSUBSCRIBE.equals(command)) {
 					logger.debug("Failed to send message to MessageChannel in session " + session.getId(), ex);
 				}
 				else if (logger.isErrorEnabled()) {
-					// Skip unsent CONNECT messages (likely auth issues)
-					if (!isConnect || sent) {
-						logger.error("Failed to send message to MessageChannel in session " + session.getId() +
-								":" + ex.getMessage());
+					// Skip for unsent CONNECT or SUBSCRIBE (likely authentication/authorization issues)
+					if (sent || !(isConnect || StompCommand.SUBSCRIBE.equals(command))) {
+						logger.error("Failed to send message to MessageChannel in session " +
+								session.getId() + ":" + ex.getMessage());
 					}
 				}
 				handleError(session, ex, message);