Use multi_compile for the SKY_LIGHTING keyword

Assets/ScriptableRenderPipeline/HDRenderPipeline/Lighting/Resources/Deferred.shader

             #pragma shader_feature _ SSS_PRE_SCATTER_TEXTURING SSS_POST_SCATTER_TEXTURING
          // #endif
 
-            #pragma shader_feature SKY_LIGHTING
+            #pragma multi_compile _ SKY_LIGHTING
 
             #pragma multi_compile _ LIGHTING_DEBUG