go-git: Crafted repositories may modify main and submodule .git directories

go-git is an extensible git implementation library written in pure Go. Prior to 5.19.1 and 6.0.0-alpha.4, a path validation issue in go-git could allow crafted repository data to affect files outside the intended checkout target, including the repository's .git directory. These validations were introduced in upstream Git years ago, so the vulnerability arose from go-git drifting from those checks. This vulnerability is fixed in 5.19.1 and 6.0.0-alpha.4.