Get rid of get_repository_root()

[KevinGDialpad]

This has returned an empty string since the script stopped running inside a git repo (see #2).

I'm pretty sure that's what creates this error in the output:

fatal: unsafe repository ('/github/workspace' is owned by someone else)
To add an exception for this directory, call:
	git config --global --add safe.directory /github/workspace

The problem is that the tests mock its return value. I'm not sure how much effort it would be to fix them.