devel/gitaly: update to 16.3.0

Required for gitlab-ce 16.3.
Use an internal libgit2 as the FreeBSD installed version is to new
but git2go does not support a newer version yet:
https://github.com/libgit2/git2go/issues/951

Changelog:
https://gitlab.com/gitlab-org/gitaly/-/blob/master/CHANGELOG.md