+doc #19429 initial merge of docs-dev and docs

akka-docs/rst/project/migration-guide-2.3.x-2.4.x.rst

@@ -673,9 +673,12 @@ Be careful to not do any operations on the ``Future[Terminated]`` using the ``sy
 as ``ExecutionContext`` as it will be shut down with the ``ActorSystem``, instead use for example
 the Scala standard library context from ``scala.concurrent.ExecutionContext.global``.
 
+::
+
     // import system.dispatcher <- this would not work
     import scala.concurrent.ExecutionContext.Implicits.global
 
     system.terminate().foreach { _ =>
       println("Actor system was shut down")
     }
+