Update tox requirement from <4 to <5 (#159)

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@0.5...4.2.6)

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

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

dev-requirements.txt

@@ -4,7 +4,7 @@ pylint
 pep257
 pydocstyle
 flake8
-tox < 4
+tox < 5
 tox-pyenv
 isort
 wheel