Pytest-find-dependencies

---------------------
Bugfix release.

Fixes
-----
* Fix crash when multiple "always failing" tests are detected (see `6`_)

Infrastructure
~~~~~~~~~~~~~~
* added pytest 7.0 to CI tests
* skip tests using ``pytest-xdist`` if it is not installed (see `7`_)

.. _`1`: https://github.com/mrbean-bremen/pytest-find-dependencies/issues/1
.. _`2`: https://github.com/mrbean-bremen/pytest-find-dependencies/issues/2
.. _`3`: https://github.com/mrbean-bremen/pytest-find-dependencies/issues/3
.. _`6`: https://github.com/mrbean-bremen/pytest-find-dependencies/issues/6
.. _`7`: https://github.com/mrbean-bremen/pytest-find-dependencies/issues/7