### 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)


static_cast<RenderGeometryInstance *>(p_tracker->userdata)->_mark_dirty();
	static_cast<GeometryInstanceForwardMobile *>(p_tracker->userdata)->data->dirty_dependencies = true;
}
bool RenderForwardMobile::is_dynamic_gi_supported() const {
	return false;
}
bool RenderForwardMobile::is_volumetric_supported() const {
	return false;
}
uint32_t RenderForwardMobile::get_max_elements() const {