### 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)


framebuffer = rb_data->get_color_fbs(RenderBufferDataForwardMobile::FB_CONFIG_THREE_SUBPASSES);
		} else {
			
			framebuffer = rb_data->get_color_fbs(RenderBufferDataForwardMobile::FB_CONFIG_TWO_SUBPASSES);
		}
	} else {
		ERR_FAIL(); 
	}
	p_render_data->scene_data->emissive_exposure_normalization = -1.0;
	RD::get_singleton()->draw_command_begin_label("Render Setup");
	_setup_lightmaps(p_render_data, *p_render_data->lightmaps, p_render_data->scene_data->cam_transform);
	_setup_environment(p_render_data, is_reflection_probe, screen_size, !is_reflection_probe, p_default_bg_color, false);
	_update_render_base_uniform_set(); 
	RD::get_singleton()->draw_command_end_label(); 
	
	RID radiance_texture;
	bool draw_sky = false;
	bool draw_sky_fog_only = false;
	
	float sky_energy_multiplier = 1.0 / _render_buffers_get_luminance_multiplier();
	Color clear_color = p_default_bg_color;
	bool keep_color = false;
	if (get_debug_draw_mode() == RS::VIEWPORT_DEBUG_DRAW_OVERDRAW) {
		clear_color = Color(0, 0, 0, 1); 
	} else if (is_environment(p_render_data->environment)) {
		RS::EnvironmentBG bg_mode = environment_get_background(p_render_data->environment);
		float bg_energy_multiplier = environment_get_bg_energy_multiplier(p_render_data->environment);
		bg_energy_multiplier *= environment_get_bg_intensity(p_render_data->environment);
		if (p_render_data->camera_attributes.is_valid()) {
			bg_energy_multiplier *= RSG::camera_attributes->camera_attributes_get_exposure_normalization_factor(p_render_data->camera_attributes);