Bump pytest-cov from 2.8.1 to 2.9.0

Bumps [pytest-cov](https://github.com/pytest-dev/pytest-cov) from 2.8.1 to 2.9.0.
- [Release notes](https://github.com/pytest-dev/pytest-cov/releases)
- [Changelog](https://github.com/pytest-dev/pytest-cov/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest-cov@v2.8.1...v2.9.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

dev-requirements.txt

@@ -23,7 +23,7 @@ pyenchant==3.1.0  # Bindings for a spellchecking sytem
 pygithub==1.51
 pylint==2.5.2  # Lint
 pyroma==2.6  # Packaging best practices checker
-pytest-cov==2.8.1  # Measure code coverage
+pytest-cov==2.9.0  # Measure code coverage
 pytest-envfiles==0.1.0  # Use files for environment variables for tests
 pytest==5.4.2  # Test runners
 sphinx-autodoc-typehints==1.10.3