sysutils/s6: Update to version 2.13.1.0

Changelog: https://git.skarnet.org/cgi-bin/cgit.cgi/s6/plain/NEWS

PR: 283100, 282021
MFH: 2024Q4
Reported by: Saj Goonatilleke <sg@redu.cx>

(cherry picked from commit 5a326a79614f751c7bee8e43c107027f3d57bbae)