python3Packages.Babel: 2.7.0 -> 2.9.0
python3Packages.Babel: 2.7.0 -> 2.9.0

Update babel as the current release is over a year old and some packages
need >=2.8.0.

Also migrate to pytestCheckHook.

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