### 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)


}
		switch (bg_mode) {
			case RS::ENV_BG_CLEAR_COLOR: {
				clear_color = p_default_bg_color;
				clear_color.r *= bg_energy_multiplier;
				clear_color.g *= bg_energy_multiplier;
				clear_color.b *= bg_energy_multiplier;
				/*
				if (p_render_data->render_buffers->has_custom_data(RB_SCOPE_FOG) || environment_get_fog_enabled(p_render_data->environment)) {
					draw_sky_fog_only = true;
					RendererRD::MaterialStorage::get_singleton()->material_set_param(sky.sky_scene_state.fog_material, "clear_color", Variant(clear_color.srgb_to_linear()));
				}
				*/
			} break;
			case RS::ENV_BG_COLOR: {
				clear_color = environment_get_bg_color(p_render_data->environment);
				clear_color.r *= bg_energy_multiplier;
				clear_color.g *= bg_energy_multiplier;
				clear_color.b *= bg_energy_multiplier;
				/*
				if (p_render_data->render_buffers->has_custom_data(RB_SCOPE_FOG) || environment_get_fog_enabled(p_render_data->environment)) {
					draw_sky_fog_only = true;
					RendererRD::MaterialStorage::get_singleton()->material_set_param(sky.sky_scene_state.fog_material, "clear_color", Variant(clear_color.srgb_to_linear()));
				}
				*/
			} break;
			case RS::ENV_BG_SKY: {
				draw_sky = true;
			} break;
			case RS::ENV_BG_CANVAS: {