Method set_error

include/exec/materialize.hpp:46–51

      template <class _Error>
      constexpr void set_error(_Error __err) noexcept
      {
        STDEXEC::set_value(static_cast<_Receiver&&>(__upstream_),
                           set_error_t(),
                           static_cast<_Error&&>(__err));
      }

      constexpr void set_stopped() noexcept
      {