### 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)


ginstance->base_flags |= INSTANCE_DATA_FLAG_MULTIMESH_HAS_COLOR;
		ginstance->base_flags |= INSTANCE_DATA_FLAG_MULTIMESH_HAS_CUSTOM_DATA;
		
		ginstance->base_flags |= (ginstance->trail_steps << INSTANCE_DATA_FLAGS_PARTICLE_TRAIL_SHIFT);
		if (!particles_storage->particles_is_using_local_coords(ginstance->data->base)) {
			store_transform = false;
		}
		ginstance->transforms_uniform_set = particles_storage->particles_get_instance_buffer_uniform_set(ginstance->data->base, scene_shader.default_shader_rd, TRANSFORMS_UNIFORM_SET);
		if (particles_storage->particles_get_frame_counter(ginstance->data->base) == 0) {
			
			particles_storage->update_particles();
		}
	} else if (ginstance->data->base_type == RS::INSTANCE_MESH) {
		if (mesh_storage->skeleton_is_valid(ginstance->data->skeleton)) {
			ginstance->transforms_uniform_set = mesh_storage->skeleton_get_3d_uniform_set(ginstance->data->skeleton, scene_shader.default_shader_rd, TRANSFORMS_UNIFORM_SET);
			if (ginstance->data->dirty_dependencies) {
				mesh_storage->skeleton_update_dependency(ginstance->data->skeleton, &ginstance->data->dependency_tracker);
			}
		} else {
			ginstance->transforms_uniform_set = RID();
		}
	}
	ginstance->store_transform_cache = store_transform;
	if (ginstance->data->dirty_dependencies) {
		ginstance->data->dependency_tracker.update_end();
		ginstance->data->dirty_dependencies = false;
	}
	ginstance->dirty_list_element.remove_from_list();
}
void RenderForwardMobile::_update_dirty_geometry_instances() {