Merge branch 'jn/remote-helpers-with-git-dir' into maint

"git ls-remote" and "git archive --remote" are designed to work without being in a directory under Git's control. However, recent updates revealed that we randomly look into a directory called .git/ without actually doing necessary set-up when working in a repository. Stop doing so. * jn/remote-helpers-with-git-dir: remote helpers: avoid blind fall-back to ".git" when setting GIT_DIR remote: avoid reading $GIT_DIR config in non-repo