python3Packages.mypy: add setuptools as native build input
python3Packages.mypy: add setuptools as native build input

because it is the build system used by mypy. In the past, the dependency
was implictly fulfilled because setuptools was added by
buildPythonPackage.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs