python312Packages.python-can: relax msgpack constraint

pkgs/development/python-modules/python-can/default.nix

···
     substituteInPlace tox.ini \
       --replace " --cov=can --cov-config=tox.ini --cov-report=lcov --cov-report=term" ""
   '';
+  pythonRelaxDeps = [ "msgpack" ];
 
   nativeBuildInputs = [ setuptools ];