### 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)


defines += "\n#define SAMPLERS_BINDING_FIRST_INDEX " + itos(SAMPLERS_BINDING_FIRST_INDEX) + "\n";
	}
#ifdef REAL_T_IS_DOUBLE
	{
		defines += "\n#define USE_DOUBLE_PRECISION \n";
	}
#endif
	scene_shader.init(defines);
	
	render_list_thread_threshold = GLOBAL_GET("rendering/limits/forward_renderer/threaded_render_minimum_instances");
	_update_shader_quality_settings();
}
RenderForwardMobile::~RenderForwardMobile() {
	RSG::light_storage->directional_shadow_atlas_set_size(0);
	
	for (uint32_t i = 0; i < render_pass_uniform_sets.size(); i++) {
		if (render_pass_uniform_sets[i].is_valid() && RD::get_singleton()->uniform_set_is_valid(render_pass_uniform_sets[i])) {
			RD::get_singleton()->free(render_pass_uniform_sets[i]);
		}
	}
	{
		for (const RID &rid : scene_state.uniform_buffers) {
			RD::get_singleton()->free(rid);
		}
		RD::get_singleton()->free(scene_state.lightmap_buffer);
		RD::get_singleton()->free(scene_state.lightmap_capture_buffer);
		memdelete_arr(scene_state.lightmap_captures);
	}
}