nixos/dokuwiki: Upgrade to PHP 8.1
nixos/dokuwiki: Upgrade to PHP 8.1

They seem to run tests against 8.1 since this commit:
https://github.com/splitbrain/dokuwiki/commit/7aee97ee813f0e08e339a6f29e554d52bc4ef9d3

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