devel/py-mdv: Exclude tests package from installation

The upstream setup.py used setuptools.find_packages() without
exclusions, which caused the top-level "tests" package to be installed
into ${PYTHON_SITELIBDIR}/tests. This violated the Python packaging
hierarchy rules and led to conflicts with other ports installing files
under the same generic directory.

Patch setup.py to exclude the "tests" package from installation.

PR: 290278
Reported by: se

(cherry picked from commit da149cc9d0b614bdbfcab3194ce215aabed12712)