VarAction2: Add support for more varaction2 types

Add CB failure and deterministic relative types

src/newgrf_extension.h

@@ -100,6 +100,7 @@ enum GRFFeatureTestObservationFlag : uint8 {
 	GFTOF_MORE_OBJECTS_PER_GRF = 0,
 	GFTOF_MORE_ACTION2_IDS,
 	GFTOF_TOWN_ZONE_CALLBACK,
+	GFTOF_MORE_VARACTION2_TYPES,
 
 	GFTOF_INVALID = 0xFF,
 };