Fix typing for lights in Scene.__init__

[maitbayev]

lights should be Optional[List[lighting.Light]] instead of Optional[lighting.Light]

[maitbayev]

cc @mikedh

[mikedh]

Thanks for the fix!! I added typeguard to check this in the future, which caught a bunch of other instances. I didn't do the whole module, but if anyone else wants to contribute typing fixes if you run tests with typeguard it catches a lot more of them:

pytest --typeguard-packages=trimesh tests