goocanvasmm2.updateScript: change version policy
goocanvasmm2.updateScript: change version policy

This package is dead and stuck on  unstable version so odd-unstable policy tried to downgrade it, even though it was intentionally pinned on unstable because no stable version is available.

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