security/gopass: Update to 1.12.4

Manpage is now installed by the make install command, there is no need to
install it in the post-build target anymore.

Changelog: https://github.com/gopasspw/gopass/blob/v1.12.4/CHANGELOG.md

Approved by: dbaio (mentor)
Differential Revision: https://reviews.freebsd.org/D29358