Fix missing ProcessAction between the last mana being paid and the spell being cast. (#13396)

This is necessary so that, among other things, the Rain of Riches watcher can see that the last mana of a spell was a Treasure before the spell is cast - at which point it needs to already have Cascade.

Mage/src/main/java/mage/players/PlayerImpl.java

@@ -1346,6 +1346,7 @@ public abstract class PlayerImpl implements Player, Serializable {
                 castEvent.setZone(fromZone);
                 game.fireEvent(castEvent);
                 if (spell.activate(game, allowedIdentifiers, noMana)) {
+                    game.processAction();
                     GameEvent castedEvent = GameEvent.getEvent(GameEvent.EventType.SPELL_CAST,
                             ability.getId(), ability, playerId, approvingObject);
                     castedEvent.setZone(fromZone);