### 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 ((1 << RS::INSTANCE_LIGHT) + (1 << RS::INSTANCE_REFLECTION_PROBE) + (1 << RS::INSTANCE_DECAL));
}
void RenderForwardMobile::GeometryInstanceForwardMobile::pair_light_instances(const RID *p_light_instances, uint32_t p_light_instance_count) {
	omni_light_count = 0;
	spot_light_count = 0;
	for (uint32_t i = 0; i < p_light_instance_count; i++) {
		RS::LightType type = RendererRD::LightStorage::get_singleton()->light_instance_get_type(p_light_instances[i]);
		switch (type) {
			case RS::LIGHT_OMNI: {
				if (omni_light_count < (uint32_t)MAX_RDL_CULL) {
					omni_lights[omni_light_count] = RendererRD::LightStorage::get_singleton()->light_instance_get_forward_id(p_light_instances[i]);
					omni_light_count++;
				}
			} break;
			case RS::LIGHT_SPOT: {
				if (spot_light_count < (uint32_t)MAX_RDL_CULL) {
					spot_lights[spot_light_count] = RendererRD::LightStorage::get_singleton()->light_instance_get_forward_id(p_light_instances[i]);
					spot_light_count++;
				}
			} break;
			default:
				break;
		}
	}
}
void RenderForwardMobile::GeometryInstanceForwardMobile::pair_reflection_probe_instances(const RID *p_reflection_probe_instances, uint32_t p_reflection_probe_instance_count) {