Fix an issue with old tox version

Author: Cito

tox.ini

@@ -59,7 +59,7 @@ deps =
     pytest-cov>=4,<7
     pytest-describe>=2,<3
     pytest-timeout>=2,<3
-    py3{6,7,8,9}, pypy39: typing-extensions>=4.2,<5
+    py3{6,7,8,9},pypy39: typing-extensions>=4.2,<5
 commands =
     # to also run the time-consuming tests: tox -e py311 -- --run-slow
     # to run the benchmarks: tox -e py311 -- -k benchmarks --benchmark-enable