Update tox requirement from ~=4.17.1 to ~=4.20.0

Updates the requirements on [tox](https://github.com/tox-dev/tox) to permit the latest version.
- [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@4.17.1...4.20.0)

---
updated-dependencies:
- dependency-name: tox
  dependency-type: direct:development
...

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

requirements-dev.txt

@@ -1,7 +1,7 @@
 build~=1.2.1
 pre-commit~=3.8.0
 twine~=5.1.1
-tox~=4.17.1
+tox~=4.20.0
 pytest~=8.3.2
 pytest-cov~=5.0.0
 pytest-resource-path~=1.3.0