### 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)


return 2.0;
}
RD::DataFormat RenderForwardMobile::_render_buffers_get_color_format() {
	
	return RD::DATA_FORMAT_A2B10G10R10_UNORM_PACK32;
}
bool RenderForwardMobile::_render_buffers_can_be_storage() {
	
	
	return false;
}
RID RenderForwardMobile::_setup_render_pass_uniform_set(RenderListType p_render_list, const RenderDataRD *p_render_data, RID p_radiance_texture, bool p_use_directional_shadow_atlas, int p_index) {
	RendererRD::LightStorage *light_storage = RendererRD::LightStorage::get_singleton();
	RendererRD::TextureStorage *texture_storage = RendererRD::TextureStorage::get_singleton();
	
	ERR_FAIL_INDEX_V(p_index, (int)scene_state.uniform_buffers.size(), RID());
	bool is_multiview = false;
	Ref<RenderBufferDataForwardMobile> rb_data;
	Ref<RenderSceneBuffersRD> rb;
	if (p_render_data && p_render_data->render_buffers.is_valid()) {
		rb = p_render_data->render_buffers;
		is_multiview = rb->get_view_count() > 1;
		if (rb->has_custom_data(RB_SCOPE_MOBILE)) {