### 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)


#include "render_forward_mobile.h"
#include "core/config/project_settings.h"
#include "core/object/worker_thread_pool.h"
#include "servers/rendering/renderer_rd/storage_rd/light_storage.h"
#include "servers/rendering/renderer_rd/storage_rd/mesh_storage.h"
#include "servers/rendering/renderer_rd/storage_rd/particles_storage.h"
#include "servers/rendering/renderer_rd/storage_rd/texture_storage.h"
#include "servers/rendering/rendering_device.h"
#include "servers/rendering/rendering_server_default.h"
using namespace RendererSceneRenderImplementation;
RendererRD::ForwardID RenderForwardMobile::ForwardIDStorageMobile::allocate_forward_id(RendererRD::ForwardIDType p_type) {
	int32_t index = -1;
	for (uint32_t i = 0; i < forward_id_allocators[p_type].allocations.size(); i++) {
		if (forward_id_allocators[p_type].allocations[i] == false) {
			index = i;
			break;
		}
	}
	if (index == -1) {
		index = forward_id_allocators[p_type].allocations.size();
		forward_id_allocators[p_type].allocations.push_back(true);
		forward_id_allocators[p_type].map.push_back(0xFF);
	} else {
		forward_id_allocators[p_type].allocations[index] = true;
	}
	return index;
}
void RenderForwardMobile::ForwardIDStorageMobile::free_forward_id(RendererRD::ForwardIDType p_type, RendererRD::ForwardID p_id) {