Update tox requirement from ~=4.11.0 to >=4.11,<4.21

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@4.11.0...4.20.0)

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

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

setup.cfg

@@ -73,7 +73,7 @@ dev =
     pre-commit~=3.3.3
     sphinx~=3.2.1
     sphinx-rtd-theme~=0.5.0
-    tox~=4.11.0
+    tox>=4.11,<4.21
     types-setuptools~=68.1.0.0
     Jinja2<3.1