security/openssh-portable: fix uidswap behavior on FreeBSD

This adds base commit 239e8c98636a757 as a patch to avoid losing our
real GID inside temporarily_use_uid()/restore_uid() blocks. This is
scoped to the specific __FreeBSD_version along 15.0 where we re-aligned
our setgroups(2)/getgroups(2) with other platforms (no egid touching;
just supplemental groups).

Approved by: bdrewery (maintainer, without version check)
Differential Revision: https://reviews.freebsd.org/D51846