I think electrical safety first says C3, but NAPIT code breakers is C2 (Presuming cable buried less than 50mm in wall). Is there any outdoor lights that are metal? That might make a difference if say a metal outside light next to a washing line poked in the ground.
Some electricians would C2 it and defend themselves reasonably, but then some C2 a plastic board, its your professional opinion so as long as you can justify it, even the experts are divided. Personally in most circumstances I would give it a C3 but would not look down on anyone that C2'd lighting without RCD protection.