Call base.AfterAll() to kill TestKit ActorSystem (#5705)

Co-authored-by: Gregorius Soedharmo <[email protected]>

Author: Arkatufus

src/core/Akka.Remote.Tests/Serialization/SerializationTransportInformationSpec.cs

@@ -181,6 +181,7 @@ public void Serialization_of_ActorRef_in_remote_message_must_resolve_Address()
 
         protected override void AfterAll()
         {
+            base.AfterAll();
             Shutdown(System2, verifySystemShutdown: true);
         }
     }