Bump tox from 4.15.0 to 4.16.0 in /requirements

Bumps [tox](https://github.com/tox-dev/tox) from 4.15.0 to 4.16.0.
- [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@4.15.0...4.16.0)

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

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

Author: dependabot[bot]

requirements/tox.txt

@@ -1,3 +1,3 @@
 -r ./coverage.txt
-tox==4.15.0
+tox==4.16.0
 tox-gh-actions==3.2.0