mail/fetchmail{,conf}: Update 6.6.6 => 6.6.7

Changelog:
https://gitlab.com/fetchmail/fetchmail/-/blob/6.6.7/NEWS#L113

PR: 298119
Reported by: Corey Halpin <chalpin@cs.wisc.edu> (maintainer)
Approved by: osa, vvd (Mentors, implicit)
MFH: 2026Q3

(cherry picked from commit b6a3a91f25d91a9789bfee57fd7595e483b863c2)