### 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)


reflection_probe_count = p_reflection_probe_instance_count < (uint32_t)MAX_RDL_CULL ? p_reflection_probe_instance_count : (uint32_t)MAX_RDL_CULL;
	for (uint32_t i = 0; i < reflection_probe_count; i++) {
		reflection_probes[i] = RendererRD::LightStorage::get_singleton()->reflection_probe_instance_get_forward_id(p_reflection_probe_instances[i]);
	}
}
void RenderForwardMobile::GeometryInstanceForwardMobile::pair_decal_instances(const RID *p_decal_instances, uint32_t p_decal_instance_count) {
	decals_count = p_decal_instance_count < (uint32_t)MAX_RDL_CULL ? p_decal_instance_count : (uint32_t)MAX_RDL_CULL;
	for (uint32_t i = 0; i < decals_count; i++) {
		decals[i] = RendererRD::TextureStorage::get_singleton()->decal_instance_get_forward_id(p_decal_instances[i]);
	}
}
void RenderForwardMobile::GeometryInstanceForwardMobile::set_softshadow_projector_pairing(bool p_softshadow, bool p_projector) {
	use_projector = p_projector;
	use_soft_shadow = p_softshadow;
}
void RenderForwardMobile::GeometryInstanceForwardMobile::_mark_dirty() {
	if (dirty_list_element.in_list()) {
		return;
	}
	
	GeometryInstanceSurfaceDataCache *surf = surface_caches;
	while (surf) {
		GeometryInstanceSurfaceDataCache *next = surf->next;
		RenderForwardMobile::get_singleton()->geometry_instance_surface_alloc.free(surf);
		surf = next;
	}
	surface_caches = nullptr;
	RenderForwardMobile::get_singleton()->geometry_instance_dirty_list.add(&dirty_list_element);
}
void RenderForwardMobile::_geometry_instance_add_surface_with_material(GeometryInstanceForwardMobile *ginstance, uint32_t p_surface, SceneShaderForwardMobile::MaterialData *p_material, uint32_t p_material_id, uint32_t p_shader_id, RID p_mesh) {