Bump tox from 3.28.0 to 4.18.1

Bumps [tox](https://github.com/tox-dev/tox) from 3.28.0 to 4.18.1.
- [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@3.28.0...4.18.1)

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

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

setup.cfg

@@ -85,7 +85,7 @@ dev =
     pre-commit~=2.20.0
     sphinx==3.2.1
     sphinxcontrib-napoleon~=0.7
-    tox~=3.28.0
+    tox>=3.28,<4.19
     flask_testing~=0.8.0
     sphinx-rtd-theme~=0.5.0
     sphinx-argparse~=0.2.5