### 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)


u.append_id(decal_atlas);
			uniforms.push_back(u);
		}
		{
			RD::Uniform u;
			u.binding = 12;
			u.uniform_type = RD::UNIFORM_TYPE_TEXTURE;
			RID decal_atlas = RendererRD::TextureStorage::get_singleton()->decal_atlas_get_texture_srgb();
			u.append_id(decal_atlas);
			uniforms.push_back(u);
		}
		{
			RD::Uniform u;
			u.binding = 13;
			u.uniform_type = RD::UNIFORM_TYPE_STORAGE_BUFFER;
			u.append_id(RendererRD::TextureStorage::get_singleton()->get_decal_buffer());
			uniforms.push_back(u);
		}
		{
			RD::Uniform u;
			u.uniform_type = RD::UNIFORM_TYPE_STORAGE_BUFFER;
			u.binding = 14;
			u.append_id(RendererRD::MaterialStorage::get_singleton()->global_shader_uniforms_get_storage_buffer());
			uniforms.push_back(u);
		}
		uniforms.append_array(material_storage->get_default_sampler_uniforms(SAMPLERS_BINDING_FIRST_INDEX));
		render_base_uniform_set = RD::get_singleton()->uniform_set_create(uniforms, scene_shader.default_shader_rd, SCENE_UNIFORM_SET);
	}
}
RID RenderForwardMobile::_render_buffers_get_normal_texture(Ref<RenderSceneBuffersRD> p_render_buffers) {