Bump tox from 4.8.0 to 4.9.0

Bumps [tox](https://github.com/tox-dev/tox) from 4.8.0 to 4.9.0.
- [Release notes](https://github.com/tox-dev/tox/releases)
- [Changelog](https://github.com/tox-dev/tox/blob/main/docs/changelog.rst)
- [Commits](tox-dev/tox@4.8.0...4.9.0)

---
updated-dependencies:
- dependency-name: tox
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

requirements_dev.txt

@@ -13,6 +13,6 @@ sphinx-rtd-theme>=0.5.0
 
 # testing
 flake8>=2.6.0
-tox==4.8.0
+tox==4.9.0
 coverage>=4.3.0
 wget>=3.2