py-build dependency circular dependency

[Leonardo Taccari <leot%NetBSD.org@localhost>]

Hello folks,
When updating py-typing-extensions to latest version I had missed a new
circular dependency in Python 3.7 introduced probably both by switch to
wheel.mk and py-flit_core tool dependency, i.e.:

 py-build -> py-importlib-metadata -> py-typing-extensions -> py-build


Any idea how to possibly address that?
Thank you!