### 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)


RendererRD::LightStorage *light_storage = RendererRD::LightStorage::get_singleton();
	
	scene_state.lightmaps_used = 0;
	for (int i = 0; i < (int)p_lightmaps.size(); i++) {
		if (i >= (int)scene_state.max_lightmaps) {
			break;
		}
		RID lightmap = light_storage->lightmap_instance_get_lightmap(p_lightmaps[i]);
		Basis to_lm = light_storage->lightmap_instance_get_transform(p_lightmaps[i]).basis.inverse() * p_cam_transform.basis;
		to_lm = to_lm.inverse().transposed(); 
		RendererRD::MaterialStorage::store_transform_3x3(to_lm, scene_state.lightmaps[i].normal_xform);
		scene_state.lightmaps[i].exposure_normalization = 1.0;
		if (p_render_data->camera_attributes.is_valid()) {
			float baked_exposure = light_storage->lightmap_get_baked_exposure_normalization(lightmap);
			float enf = RSG::camera_attributes->camera_attributes_get_exposure_normalization_factor(p_render_data->camera_attributes);
			scene_state.lightmaps[i].exposure_normalization = enf / baked_exposure;
		}
		scene_state.lightmap_ids[i] = p_lightmaps[i];
		scene_state.lightmap_has_sh[i] = light_storage->lightmap_uses_spherical_harmonics(lightmap);
		scene_state.lightmaps_used++;
	}
	if (scene_state.lightmaps_used > 0) {
		RD::get_singleton()->buffer_update(scene_state.lightmap_buffer, 0, sizeof(LightmapData) * scene_state.lightmaps_used, scene_state.lightmaps, RD::BARRIER_MASK_RASTER);
	}
}
void RenderForwardMobile::_pre_opaque_render(RenderDataRD *p_render_data) {