### 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)


return RID();
}
RID RenderForwardMobile::_render_buffers_get_velocity_texture(Ref<RenderSceneBuffersRD> p_render_buffers) {
	return RID();
}
_FORCE_INLINE_ static uint32_t _indices_to_primitives(RS::PrimitiveType p_primitive, uint32_t p_indices) {
	static const uint32_t divisor[RS::PRIMITIVE_MAX] = { 1, 2, 1, 3, 1 };
	static const uint32_t subtractor[RS::PRIMITIVE_MAX] = { 0, 0, 1, 0, 1 };
	return (p_indices - subtractor[p_primitive]) / divisor[p_primitive];
}
void RenderForwardMobile::_fill_render_list(RenderListType p_render_list, const RenderDataRD *p_render_data, PassMode p_pass_mode, bool p_append) {
	RendererRD::MeshStorage *mesh_storage = RendererRD::MeshStorage::get_singleton();
	if (p_render_list == RENDER_LIST_OPAQUE) {
		scene_state.used_sss = false;
		scene_state.used_screen_texture = false;
		scene_state.used_normal_texture = false;
		scene_state.used_depth_texture = false;
	}
	uint32_t lightmap_captures_used = 0;
	Plane near_plane(-p_render_data->scene_data->cam_transform.basis.get_column(Vector3::AXIS_Z), p_render_data->scene_data->cam_transform.origin);
	near_plane.d += p_render_data->scene_data->cam_projection.get_z_near();
	float z_max = p_render_data->scene_data->cam_projection.get_z_far() - p_render_data->scene_data->cam_projection.get_z_near();
	RenderList *rl = &render_list[p_render_list];
	
	_update_dirty_geometry_instances();
	if (!p_append) {
		rl->clear();
		if (p_render_list == RENDER_LIST_OPAQUE) {
			render_list[RENDER_LIST_ALPHA].clear(); 
		}