[3.11] gh-104874: Document NewType.__supertype__ (GH-104875) (#104907)

gh-104874: Document NewType.__supertype__ (GH-104875)
(cherry picked from commit 41768a2bd3a8f57e6ce4e4ae9cab083b69817ec1)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
2 files changed