mcfgthreads: fix syntax
mcfgthreads: fix syntax

PR #115603 / 8ad96b7786134cba3d856ad5572080cef94f1640 introduced a
syntax error by introducing an '' inside an indented string and thus a
syntax error. Was merged despite the failing ofborg check.

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