nixos/udev: use udevadm from buildPackages to fix cross (#431144)

nixos/modules/services/hardware/udev.nix

···
           # We only include the out output here to avoid needing to include all
           # other outputs in the installer tests as well
           # We only need the udevadm command anyway
-          pkgs.systemdMinimal.out
+          pkgs.buildPackages.systemdMinimal.out
         ];
       }
       ''