[STX] Implemented Retriever Phoenix

Mage/src/main/java/mage/game/events/GameEvent.java

@@ -301,6 +301,7 @@ public class GameEvent implements Serializable {
         DIDNT_PAY_CUMULATIVE_UPKEEP,
         LIFE_PAID,
         CASCADE_LAND,
+        LEARN,
         //permanent events
         ENTERS_THE_BATTLEFIELD_SELF, /* 616.1a If any of the replacement and/or prevention effects are self-replacement effects (see rule 614.15),
                                         one of them must be chosen. If not, proceed to rule 616.1b. */