Missing creation of second actor (#28251)

* Update ActorHierarchyExperiments.java

Missing creation of second actor:
context.spawn(StartStopActor2.create(), "second");

* sbt akka-docs/test:javafmt

akka-docs/src/test/java/jdocs/typed/tutorial_1/ActorHierarchyExperiments.java

@@ -55,6 +55,8 @@ class StartStopActor1 extends AbstractBehavior<String> {
   private StartStopActor1(ActorContext<String> context) {
     super(context);
     System.out.println("first started");
+
+    context.spawn(StartStopActor2.create(), "second");
   }
 
   @Override