Update pytest-doctestplus to 0.9.0

[pyup-bot]

This PR updates pytest-doctestplus from 0.5.0 to 0.9.0.

Changelog

0.9.0

==================

- Declare ``setuptools`` runtime dependency [93]

- Add ``SHOW_WARNINGS`` flag to show warnings. [136]

- Add the doctestplus sphinx extension. [113]

- Compatibility with pytest>=6.3 [140, 141]

0.8.0

==================

- Compatibility with ``pytest`` 6.0.0. [120]

0.7.0

==================

- Added a new ini option, ``doctest_subpackage_requires``, that can be used to skip
specific subpackages based on required packages. [112]

0.6.1

==================

- Disabling the usage of the ``doctest_ignore_import_errors`` option to
ensure no behaviour changes compared to the 0.5.0 release. [108]

0.6.0

==================

- Drop support for ``python`` versions earlier than 3.6. [103]

- Drop support for ``pytest`` versions earlier than 4.0. [103]

- Fix compatibility with ``pytest`` 5.4. [103]

Links

• PyPI: https://pypi.org/project/pytest-doctestplus
• Changelog: https://pyup.io/changelogs/pytest-doctestplus/
• Repo: https://github.com/astropy/pytest-doctestplus