dxil_nir_lower_int_cubemaps: When not lowering samplers, don't touch sampler types
Otherwise we end up converting the sampler type from cube -> 2D, without modifying the coordinates, which means that all texture lookups would be wrong. Untestable until !18022 (merged) lands since this pass only modifies integer cubemaps, and integer texture sampling of any kind isn't supported until shader model 6.7.
/cc @kusma as the author of !16904 (merged)