mail/fetchmail{,conf}: Update 6.6.5 => 6.6.6 (critical bugfix for imap)
Changelog:
https://gitlab.com/fetchmail/fetchmail/-/blob/6.6.6/NEWS#L110
PR: 296262
Sponsored by: UNIS Labs
MFH: 2026Q2
(cherry picked from commit 44305833bada607f8dd6ce2a649f11ffb3ed471e)