### 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)


if (render_buffers) {
		
		free_data();
	}
	render_buffers = p_render_buffers;
	ERR_FAIL_NULL(render_buffers); 
}
RID RenderForwardMobile::RenderBufferDataForwardMobile::get_color_fbs(FramebufferConfigType p_config_type) {
	ERR_FAIL_NULL_V(render_buffers, RID());
	RendererRD::TextureStorage *texture_storage = RendererRD::TextureStorage::get_singleton();
	ERR_FAIL_NULL_V(texture_storage, RID());
	
	
	
	
	RS::ViewportMSAA msaa_3d = render_buffers->get_msaa_3d();
	bool use_msaa = msaa_3d != RS::VIEWPORT_MSAA_DISABLED;
	uint32_t view_count = render_buffers->get_view_count();
	RID vrs_texture;
	if (render_buffers->has_texture(RB_SCOPE_VRS, RB_TEXTURE)) {
		vrs_texture = render_buffers->get_texture(RB_SCOPE_VRS, RB_TEXTURE);
	}
	Vector<RID> textures;
	int color_buffer_id = 0;
	textures.push_back(use_msaa ? render_buffers->get_color_msaa() : render_buffers->get_internal_texture()); 
	textures.push_back(use_msaa ? render_buffers->get_depth_msaa() : render_buffers->get_depth_texture()); 
	if (vrs_texture.is_valid()) {