nixos/partition-manager: switch to qt6

nixos/modules/programs/partition-manager.nix

···
     programs.partition-manager = {
       enable = lib.mkEnableOption "KDE Partition Manager";
 
-      package = lib.mkPackageOption pkgs [ "libsForQt5" "partitionmanager" ] { };
+      package = lib.mkPackageOption pkgs [ "kdePackages" "partitionmanager" ] { };
     };
   };