We were passing the complete TemporaryDirectory object to the repo clone
function instead of just the path string, resulting in the repo being
cloned into a local dir "<TemporaryDirectory '/tmp/tmphwakypf8'>".

Fix this to actually use the generated temp dir.

This change makes it necessary to keep the TemporaryDirectory object
reference until we don't need the directory anymore, otherwise it will
be removed immediately.