add python and tox to dev env

Without tox any python `scripts/make-python-env.sh` does not run. Maybe
at some point we can even generate the environment for testing with
`venvHook` like functionality.

Author: Septias

flake.nix

@@ -555,6 +555,8 @@
               cargo-nextest
               perl # needed to build vendored OpenSSL
               git-cliff
+              python311
+              python311Packages.tox
             ];
           };
       }