Newer version of the project is migrated to pyproject.toml, this change
may help to prepare for the future upgrade.
* gnu/packages/python-xyz.scm (python-partd) [build-system]: Swap to
pyproject-build-system, allowing to detect tests and run them.
Change-Id: Ia4375b83cea6dcbf7781b3dc40f544261075d2ca