Fix missing import for new package on enemy CVs.

Fixes https://github.com/Khopa/dcs_liberation/issues/570

(cherry picked from commit e887082501b88ae7b13edc1016e3926cb18e1eb8)

game/theater/controlpoint.py

@@ -530,6 +530,7 @@ class NavalControlPoint(ControlPoint, ABC):
 
     def mission_types(self, for_player: bool) -> Iterator[FlightType]:
         yield from super().mission_types(for_player)
+        from gen.flights.flight import FlightType
         if self.is_friendly(for_player):
             yield from [
                 # TODO: FlightType.INTERCEPTION