mail/notmuch-mutt: Unbreak build when PREFIX != LOCALBASE

> Generating temporary packing list

[...]
mkdir -p /wrkdirs/usr/ports/mail/notmuch-mutt/work/stage/prefix/notmuch-mutt-0.28/etc/Muttrc.d
install -m 644 notmuch-mutt.rc /wrkdirs/usr/ports/mail/notmuch-mutt/work/stage/prefix/notmuch-mutt-0.28/etc/Muttrc.d/notmuch-mutt.rc
mv: rename /wrkdirs/usr/ports/mail/notmuch-mutt/work/stage/usr/local/etc/Muttrc.d/notmuch-mutt.rc to /wrkdirs/usr/ports/mail/notmuch-mutt/work/stage/prefix/notmuch-mutt-0.28/share/examples/notmuch/notmuch-mutt.rc: No such file or directory

PR: 232310