### Godot version

4.0 Stable

### System information

Ubuntu 22.04

### Issue description

Setting fog_affect_sky = 1 do not have the desired effect when using a Color sky mode. It works properly if we use a procedural sky or the forward+ renderer.

![Screenshot from 2023-03-03 16-50-53](https://user-images.githubusercontent.com/8985409/222870514-0195c4cb-bbca-4e9b-bb6a-6e2a568d2f7b.png)


### Steps to reproduce

Add a sky with a plain color mode like the Clear Color default option. Enable fog and set fog_affect_sky value to 1. Sky is still not affected by fog. 

### Minimal reproduction project
[mobile_fog_sky_bug.zip](https://github.com/godotengine/godot/files/10887265/mobile_fog_sky_bug.zip)


for (uint32_t k = 0; k < surface_count; k++) {
						_geometry_instance_add_surface(ginstance, k, materials[k], mesh);
					}
				}
			}
			ginstance->instance_count = particles_storage->particles_get_amount(ginstance->data->base, ginstance->trail_steps);
		} break;
		default: {
		}
	}
	
	bool store_transform = true;
	ginstance->base_flags = 0;
	if (ginstance->data->base_type == RS::INSTANCE_MULTIMESH) {
		ginstance->base_flags |= INSTANCE_DATA_FLAG_MULTIMESH;
		if (mesh_storage->multimesh_get_transform_format(ginstance->data->base) == RS::MULTIMESH_TRANSFORM_2D) {
			ginstance->base_flags |= INSTANCE_DATA_FLAG_MULTIMESH_FORMAT_2D;
		}
		if (mesh_storage->multimesh_uses_colors(ginstance->data->base)) {
			ginstance->base_flags |= INSTANCE_DATA_FLAG_MULTIMESH_HAS_COLOR;
		}
		if (mesh_storage->multimesh_uses_custom_data(ginstance->data->base)) {
			ginstance->base_flags |= INSTANCE_DATA_FLAG_MULTIMESH_HAS_CUSTOM_DATA;
		}
		ginstance->transforms_uniform_set = mesh_storage->multimesh_get_3d_uniform_set(ginstance->data->base, scene_shader.default_shader_rd, TRANSFORMS_UNIFORM_SET);
	} else if (ginstance->data->base_type == RS::INSTANCE_PARTICLES) {
		ginstance->base_flags |= INSTANCE_DATA_FLAG_MULTIMESH;
		if (false) { 
			ginstance->base_flags |= INSTANCE_DATA_FLAG_MULTIMESH_FORMAT_2D;
		}