SPIGOT-6663: Chicken Jockeys chickens don't despawn

By: md_5 <git@md-5.net>

paper-server/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java

@@ -661,7 +661,7 @@ public class CraftEventFactory {
         org.bukkit.entity.AnimalTamer bukkitTamer = (tamer != null ? tamer.getBukkitEntity() : null);
         CraftServer craftServer = (CraftServer) bukkitEntity.getServer();
 
-        entity.persistenceRequired = true;
+        entity.setPersistenceRequired(true);
 
         EntityTameEvent event = new EntityTameEvent((LivingEntity) bukkitEntity, bukkitTamer);
         craftServer.getPluginManager().callEvent(event);