BUG - AI freezing when blocking derevi

I'm getting AI freezing when it attempts to block when I attack with [[Derevi, Empyrial Tactician]] on the battlefield.

I get the following in the server log:

```
=>[CALL - 5] ThreadExecutorImpl$CachedThreadPoolWithException.afterExecute
java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
at java.util.ArrayList$Itr.next(ArrayList.java:859)
at mage.util.CardUtil.deepCopyList(CardUtil.java:2036)
at mage.util.CardUtil.deepCopyObject(CardUtil.java:1988)
at mage.abilities.TriggeredAbilities.(TriggeredAbilities.java:66)
at mage.abilities.TriggeredAbilities.copy(TriggeredAbilities.java:319)
at mage.game.GameState.(GameState.java:169)
at mage.game.GameState.copy(GameState.java:289)
at mage.game.GameImpl.(GameImpl.java:209)
at mage.game.GameCommanderImpl.(GameCommanderImpl.java:41)
at mage.game.CommanderDuel.(CommanderDuel.java:17)
at mage.game.CommanderDuel.copy(CommanderDuel.java:32)
at mage.game.CommanderDuel.copy(CommanderDuel.java:10)
at mage.server.game.GameSessionPlayer.prepareGameView(GameSessionPlayer.java:214)
at mage.server.game.GameSessionPlayer.getGameView(GameSessionPlayer.java:200)
at mage.server.game.GameSessionWatcher.lambda$update$0(GameSessionWatcher.java:56)
at java.util.Optional.ifPresent(Optional.java:159)
at mage.server.game.GameSessionWatcher.update(GameSessionWatcher.java:56)
at mage.server.game.GameController.updateGame(GameController.java:823)
at mage.server.game.GameController.lambda$init$3aa0d15c$1(GameController.java:123)
at mage.game.events.EventDispatcher.fireEvent(EventDispatcher.java:28)
at mage.game.events.TableEventSource.fireTableEvent(TableEventSource.java:44)
at mage.game.GameImpl.fireUpdatePlayersEvent(GameImpl.java:3198)
at mage.game.GameImpl.rollbackTurns(GameImpl.java:4020)
at mage.server.game.GameController.sendPlayerAction(GameController.java:539)
at mage.server.game.GameManagerImpl.sendPlayerAction(GameManagerImpl.java:127)
at mage.server.MageServerImpl.lambda$null$39(MageServerImpl.java:827)
at java.util.Optional.ifPresent(Optional.java:159)
at mage.server.MageServerImpl.lambda$sendPlayerAction$40(MageServerImpl.java:825)
at mage.server.MageServerImpl.lambda$execute$69(MageServerImpl.java:1168)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
```