Update scala-library to 2.13.8 (#31111)

* Update scala-library to 2.13.8
* Deal with some new deprecation errors
* Remove test for deprecated feature
Co-authored-by: Arnout Engelen <arnout@bzzt.net>

akka-docs/src/test/java/jdocs/dispatcher/MyUnboundedMailbox.java

@@ -41,7 +41,7 @@ public class MyUnboundedMailbox
     }
 
     public void cleanUp(ActorRef owner, MessageQueue deadLetters) {
-      while(!queue.isEmpty()) {
+      while (!queue.isEmpty()) {
         deadLetters.enqueue(owner, dequeue());
       }
     }