main/py3-gpep517: upgrade to 15
https://github.com/projg2/gpep517/blob/v15/README.rst#change-log
mostly support for py3.12 and gentoo-oriented prefix rewriting feature
Edited by Patrycja Rosa
https://github.com/projg2/gpep517/blob/v15/README.rst#change-log
mostly support for py3.12 and gentoo-oriented prefix rewriting feature