devel/py-setuptools-gettext: Update to 0.1.18

• Switch to DISTVERSION to follow Porter's Handbook: https://docs.freebsd.org/en/books/porters-handbook/book/#makefile-versions
• Switch to pep517
• Add tests (pytest)
• Fix tests requirement by patch: "Fix import failure with setuptools < 69.0 (setuptools.modified)"
• Take maintainership

ChangeLog: https://github.com/breezy-team/setuptools-gettext/releases/tag/v0.1.18
PR: 297482
Reviewed by: michaelo