Generate dependency tarball

[catfromplan9]

Hello, I'm packaging gomuks on gentoo, and to build gomuks within portage I need a dependency tarball.

I would appreciate if you updated your CI/CD to do this:

GOMODCACHE="${PWD}"/go-mod go mod download -modcacherw -x
tar --create --auto-compress --file gomuks-${VERSION}-deps.tar.xz go-mod

and attach that tarball to each release