Merge pull request #1230 from jazzband/dependabot/pip/tox-4.21.0

chore(deps): bump tox from 4.20.0 to 4.21.0

Author: aleksihakli

requirements.txt

@@ -2,4 +2,4 @@
 -r requirements-qa.txt
 -r requirements-test.txt
 sphinx_rtd_theme==2.0.0
-tox==4.20.0
+tox==4.21.0