Bump vulture from 2.0 to 2.1

Bumps [vulture](https://github.com/jendrikseipp/vulture) from 2.0 to 2.1.
- [Release notes](https://github.com/jendrikseipp/vulture/releases)
- [Changelog](https://github.com/jendrikseipp/vulture/blob/master/CHANGELOG.md)
- [Commits](jendrikseipp/vulture@v2.0...v2.1)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

dev-requirements.txt

@@ -28,5 +28,5 @@ sphinx-autodoc-typehints==1.11.0
 sphinxcontrib-spelling==5.3.0
 twine==3.2.0
 versioneer==0.18
-vulture==2.0
+vulture==2.1
 yapf==0.30.0  # Automatic formatting for Python