CastXML: refactor to avoid python2 dependency (#101996)
CastXML: refactor to avoid python2 dependency (#101996)

Switch pythonPackages.sphinx to python3Packages.sphinx. Should
only affect the build of the man-page.
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