### 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)


RID sky_rid = environment_get_sky(p_render_data->environment);
			if (sky_rid.is_valid()) {
				sky.update_radiance_buffers(rb, p_render_data->environment, p_render_data->scene_data->cam_transform.origin, time, sky_energy_multiplier);
				radiance_texture = sky.sky_get_radiance_texture_rd(sky_rid);
			} else {
				
				draw_sky = false;
			}
			if (draw_sky || draw_sky_fog_only) {
				
				sky.update_res_buffers(rb, p_render_data->environment, time, sky_energy_multiplier);
			}
			RD::get_singleton()->draw_command_end_label(); 
		}
	} else {
		clear_color = p_default_bg_color;
	}
	_pre_opaque_render(p_render_data);
	uint32_t spec_constant_base_flags = 0;
	{
		
		if (p_render_data->directional_light_count > 0) {
			if (p_render_data->directional_light_soft_shadows) {
				spec_constant_base_flags |= 1 << SPEC_CONSTANT_USING_DIRECTIONAL_SOFT_SHADOWS;
			}
		} else {
			spec_constant_base_flags |= 1 << SPEC_CONSTANT_DISABLE_DIRECTIONAL_LIGHTS;
		}
		if (!is_environment(p_render_data->environment) || !environment_get_fog_enabled(p_render_data->environment)) {
			spec_constant_base_flags |= 1 << SPEC_CONSTANT_DISABLE_FOG;