### 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)


RENDER_TIMESTAMP("Setup Rendering UV2");
	RD::get_singleton()->draw_command_begin_label("Render UV2");
	_update_render_base_uniform_set();
	RenderSceneDataRD scene_data;
	scene_data.dual_paraboloid_side = 0;
	scene_data.material_uv2_mode = true;
	scene_data.emissive_exposure_normalization = -1.0;
	RenderDataRD render_data;
	render_data.scene_data = &scene_data;
	render_data.instances = &p_instances;
	_setup_environment(&render_data, true, Vector2(1, 1), false, Color());
	PassMode pass_mode = PASS_MODE_DEPTH_MATERIAL;
	_fill_render_list(RENDER_LIST_SECONDARY, &render_data, pass_mode);
	render_list[RENDER_LIST_SECONDARY].sort_by_key();
	_fill_element_info(RENDER_LIST_SECONDARY);
	RID rp_uniform_set = _setup_render_pass_uniform_set(RENDER_LIST_SECONDARY, nullptr, RID());
	RENDER_TIMESTAMP("Render 3D Material");
	{
		RenderListParameters render_list_params(render_list[RENDER_LIST_SECONDARY].elements.ptr(), render_list[RENDER_LIST_SECONDARY].element_info.ptr(), render_list[RENDER_LIST_SECONDARY].elements.size(), true, pass_mode, rp_uniform_set, true, false);
		
		Vector<Color> clear = {
			Color(0, 0, 0, 0),
			Color(0, 0, 0, 0),
			Color(0, 0, 0, 0),