As witch huts use flag "liquid_surface", place_on only can be water. If we want on-shore witch huts, this needs to be solved differently.
Also, probably no witch huts in deep ocean swamp water?
Reviewed-on: VoxeLibre/VoxeLibre#4605
Reviewed-by: Mikita Wiśniewski <rudzik8@protonmail.com>
Co-authored-by: kno10 <erich.schubert@gmail.com>
Co-committed-by: kno10 <erich.schubert@gmail.com>