### 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)


if (pipeline_rd != prev_pipeline_rd) {
			
			
			RD::get_singleton()->draw_list_bind_render_pipeline(draw_list, pipeline_rd);
			prev_pipeline_rd = pipeline_rd;
		}
		if (xforms_uniform_set.is_valid() && prev_xforms_uniform_set != xforms_uniform_set) {
			RD::get_singleton()->draw_list_bind_uniform_set(draw_list, xforms_uniform_set, TRANSFORMS_UNIFORM_SET);
			prev_xforms_uniform_set = xforms_uniform_set;
		}
		if (material_uniform_set != prev_material_uniform_set) {
			
			if (material_uniform_set.is_valid() && RD::get_singleton()->uniform_set_is_valid(material_uniform_set)) { 
				RD::get_singleton()->draw_list_bind_uniform_set(draw_list, material_uniform_set, MATERIAL_UNIFORM_SET);
			}
			prev_material_uniform_set = material_uniform_set;
		}
		RD::get_singleton()->draw_list_set_push_constant(draw_list, &push_constant, sizeof(GeometryInstanceForwardMobile::PushConstant));
		uint32_t instance_count = surf->owner->instance_count > 1 ? surf->owner->instance_count : 1;
		if (surf->flags & GeometryInstanceSurfaceDataCache::FLAG_USES_PARTICLE_TRAILS) {
			instance_count /= surf->owner->trail_steps;
		}
		RD::get_singleton()->draw_list_draw(draw_list, index_array_rd.is_valid(), instance_count);
	}
	
	if (should_request_redraw) {
		RenderingServerDefault::redraw_request();
	}
}
RenderGeometryInstance *RenderForwardMobile::geometry_instance_create(RID p_base) {