Bump packaging from 20.9 to 21.0

Bumps [packaging](https://github.com/pypa/packaging) from 20.9 to 21.0.
- [Release notes](https://github.com/pypa/packaging/releases)
- [Changelog](https://github.com/pypa/packaging/blob/main/CHANGELOG.rst)
- [Commits](pypa/packaging@20.9...21.0)

---
updated-dependencies:
- dependency-name: packaging
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

requirements-dev.txt

@@ -1,6 +1,6 @@
 -r requirements-test.txt
 black==21.6b0
-packaging==20.9
+packaging==21.0
 pre-commit~=2.13
 PyGithub~=1.54
 pyupgrade~=2.20