Bump tox from 3.23.1 to 3.24.0 (#600)

Bumps [tox](https://github.com/tox-dev/tox) from 3.23.1 to 3.24.0.
- [Release notes](https://github.com/tox-dev/tox/releases)
- [Changelog](https://github.com/tox-dev/tox/blob/master/docs/changelog.rst)
- [Commits](tox-dev/tox@3.23.1...3.24.0)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

requirements/ci.txt

@@ -1,6 +1,6 @@
 codecov==2.1.11
 docutils==0.17.1
-tox==3.23.1
+tox==3.24.0
 tox-travis==0.12
 pygments==2.9.0
 aiohttp==3.7.4.post0