### 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)


light_storage->update_light_buffers(p_render_data, *p_render_data->lights, p_render_data->scene_data->cam_transform, p_render_data->shadow_atlas, using_shadows, directional_light_count, positional_light_count, p_render_data->directional_light_soft_shadows);
	texture_storage->update_decal_buffer(*p_render_data->decals, p_render_data->scene_data->cam_transform);
	p_render_data->directional_light_count = directional_light_count;
}
void RenderForwardMobile::_render_scene(RenderDataRD *p_render_data, const Color &p_default_bg_color) {
	RendererRD::LightStorage *light_storage = RendererRD::LightStorage::get_singleton();
	ERR_FAIL_NULL(p_render_data);
	Ref<RenderSceneBuffersRD> rb = p_render_data->render_buffers;
	ERR_FAIL_COND(rb.is_null());
	Ref<RenderBufferDataForwardMobile> rb_data;
	if (rb->has_custom_data(RB_SCOPE_MOBILE)) {
		
		
		rb_data = rb->get_custom_data(RB_SCOPE_MOBILE);
	}
	bool is_reflection_probe = p_render_data->reflection_probe.is_valid();
	RENDER_TIMESTAMP("Prepare 3D Scene");
	_update_vrs(rb);
	RENDER_TIMESTAMP("Setup 3D Scene");
	/* TODO
	// check if we need motion vectors
	if (get_debug_draw_mode() == RS::VIEWPORT_DEBUG_DRAW_MOTION_VECTORS) {
		p_render_data->scene_data->calculate_motion_vectors = true;
	} else if (render target has velocity override) { // TODO
		p_render_data->scene_data->calculate_motion_vectors = true;
	} else {
		p_render_data->scene_data->calculate_motion_vectors = false;
	}
	*/
	p_render_data->scene_data->calculate_motion_vectors = false;