sbcl: fix comment s/zlib/zstd

    # Declare at the point of actual use in case the caller wants to override

    # buildInputs to sidestep this.

    assert lib.assertMsg (!purgeNixReferences) ''

      Cannot enable coreCompression when purging Nix references, because compression requires linking in zlib

      Cannot enable coreCompression when purging Nix references, because compression requires linking in zstd

    '';

    [ zstd ]

  );