[pkg-go] Bug#979315: Add github.com/libgit2/git2go/v31 import path also

[Pirate Praveen]

Package: golang-gopkg-libgit2-git2go.v31
Version: 31.4.3-2
Severity: important

It now provides versioned import path in upstream itself

https://salsa.debian.org/go-team/packages/golang-gopkg-libgit2-git2go/-/blob/3968f20c39f0902693aef2587600e79b9ed2fe48/go.mod

module github.com/libgit2/git2go/v31

Please provide this import path in addition to the gopkg.in