[tests] use `source_pkgs` instead of `source` for correct paths
[tests] use `source_pkgs` instead of `source` for correct paths

When using `source`, the outputs seem to be relative to the source
directory, while they are correct (at least from the POV of pycharm)
with `source_pkgs`.

agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft