================
- Use GitHub actions as CI.
- Add support for Python 3.9 and 3.10.
- Drop support for Python 3.6.
- Add a workaround for
`4 <https://github.com/gocept/gocept.pytestlayer/issues/4>`_: Use
``gcoept.pytestlayer.doctest.DocTestSuite`` instead of
``doctest.DocTestSuite`` to circumvent the issue.