### 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)


}
		reverse_cull = true;
		using_subpass_transparent = true; 
		using_subpass_post_process = false; 
	} else if (rb_data.is_valid()) {
		
		screen_size = p_render_data->render_buffers->get_internal_size();
		if (rb->get_scaling_3d_mode() != RS::VIEWPORT_SCALING_3D_MODE_OFF) {
			
			using_subpass_post_process = false;
		} else if (p_render_data->environment.is_valid() && (environment_get_glow_enabled(p_render_data->environment) || RSG::camera_attributes->camera_attributes_uses_auto_exposure(p_render_data->camera_attributes) || RSG::camera_attributes->camera_attributes_uses_dof(p_render_data->camera_attributes))) {
			
			using_subpass_post_process = false;
		}
		if (scene_state.used_screen_texture || scene_state.used_depth_texture) {
			
			using_subpass_transparent = false;
			using_subpass_post_process = false;
		}
		
		RID four_subpasses = rb_data->get_color_fbs(RenderBufferDataForwardMobile::FB_CONFIG_FOUR_SUBPASSES);
		if (using_subpass_post_process && four_subpasses.is_null()) {
			
			using_subpass_post_process = false;
		}
		if (using_subpass_post_process) {
			
			framebuffer = four_subpasses;
		} else if (using_subpass_transparent) {