Deprecation warning from Pytest

[akaihola]

In recent Darker Pytest runs we have:

_pytest/nodes.py:146: 43 warnings
  _pytest/nodes.py:146: PytestDeprecationWarning: <class 'pytest_darker.DarkerItem'> is not using a cooperative constructor and only takes {'fspath', 'parent'}.
  See https://docs.pytest.org/en/stable/deprecations.html#constructors-of-custom-pytest-node-subclasses-should-take-kwargs for more details.
    warnings.warn(

_pytest/nodes.py:672: 43 warnings
  _pytest/nodes.py:672: PytestRemovedIn8Warning: The (fspath: py.path.local) argument to DarkerItem is deprecated. Please use the (path: pathlib.Path) argument instead.
  See https://docs.pytest.org/en/latest/deprecations.html#fspath-argument-for-node-constructors-replaced-with-pathlib-path
    super().__init__(

_pytest/nodes.py:708
  _pytest/nodes.py:708: PytestWarning: DarkerItem is an Item subclass and should not be a collector, however its bases File are collectors.
  Please split the Collectors and the Item into separate node types.
  Pytest Doc example: https://docs.pytest.org/en/latest/example/nonpython.html
  example pull request on a plugin: https://github.com/asmeurer/pytest-flakes/pull/40/
    warnings.warn(