Upgrade dependencies and various fixes

* Remove usage of removed `org.springframework.util.SocketUtils`
in favor of OS-selected port
* Migrate mail tests to Greenmail instead of already obsolete (and soon to be removed)
`org.springframework.integration.test.mail.TestMailServer`

basic/tcp-broadcast/src/main/java/org/springframework/integration/samples/tcpbroadcast/TcpBroadcastApplication.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018 the original author or authors.
+ * Copyright 2018-2022 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.
@@ -98,7 +98,7 @@ public class TcpBroadcastApplication {
 		}
 
 		/*
-		 * Excutor for clients.
+		 * Executor for clients.
 		 */
 		@Bean
 		public ThreadPoolTaskExecutor exec() {