No git repo found on windows (only) for package_verbose test

[dekellum]

This was discovered with testing for #5786. See that discussion. At present on master, the package::package_verbose test is not engaging, on windows only, the check_not_dirty function of cargo_package for a sub-package, even though the sub-package is in a git repo. On other platforms the (parent) repo is found and the dirty check occurs.

[dekellum]

Assign to @dekellum.

[dekellum]

Wondering if this relates to alexcrichton/git2-rs#334

[dekellum]

According to @ehuss (in #5820), alexcrichton/git2-rs#334 is the root cause.