Fix phase for TaskScheduler instances in tests

Related to: #8856

Many tests create their own `ThreadPoolTaskScheduler` beans.
Therefore, its default phase might affect the memory and performance.

* Use `phase = SmartLifecycle.DEFAULT_PHASE / 2` for manual
 `ThreadPoolTaskScheduler` beans
* Migrate affected tests classes to JUnit 5
* Make some other configuration adjustments for better performance

**Cherry-pick to `6.2.x`**

spring-integration-jms/src/test/java/org/springframework/integration/jms/JmsOutboundGatewayTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 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.
@@ -149,6 +149,7 @@ public class JmsOutboundGatewayTests extends ActiveMQMultiContextTests {
 		finally {
 			gateway.stop();
 			exec.shutdownNow();
+			taskScheduler.destroy();
 		}
 	}