Some Git-related tests required external configuration of email and
name. This forced tweaks in CI and other environments to have those set
globally before running tests.

This change makes this self-contained: Git repositories created part
of the test suite are going to automatically set a default email and
name.

Use `git_path` helper instead of `Process.quote` as was incorrect in that
context.

Looking at other examples it appears to be the correct method to use,
even when dealing with nested `Dir.cd` operations.