openscenegraph: update to 3.6.3

[luzpaz]

https://github.com/openscenegraph/OpenSceneGraph/releases/tag/OpenSceneGraph-3.6.3

[mrl5]

hello @luzpaz - if you'd like to report a bug kindly use https://bugs.funtoo.org/

you can also reach us on Discord - for more info check https://www.funtoo.org/Welcome