archivers/py-borgbackup: update to 1.4.2

Changelog: https://borgbackup.readthedocs.io/en/1.4.2/changes.html#version-1-4-2-2025-10-31

This reverts the setuptools update for the SPDX license documentation,
which would break with our ancient setuptools.

(Note that https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=270358 and
https://reviews.freebsd.org/D46236 have not made progress in over one
and a half years, so... we need to work around that.)