build: test Python 3 using GitHub Actions-based CI

PR-URL: https://github.com/nodejs/node/pull/29474


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>