Function git_checkout 

fn git_checkout<'a>(
    build_runner: &BuildRunner<'_, '_>,
    pkg_root: &'a Path,
) -> Option<(&'a Path, &'a str)>

Finds the checkout root and revision directory name of a git dependency.

This is built under this layout: $CARGO_HOME/git/checkouts/<repo>-<hash>[-shallow]/<rev>.

None when the package does not live under the global git checkouts directory, for example a vendored git dependency.