Deprecation warning for VectorizedArrayIterator.

[bangerth]

One of the CI checks for #16865 fails because of the following warning-turned-error that is unrelated to the actual changes in #16865 but just happens to be triggered there (this is apparently not used anywhere else):

/Users/runner/work/dealii/dealii/include/deal.II/base/vectorization.h:141:3: error: definition of implicit copy constructor for 'VectorizedArrayIterator<dealii::VectorizedArray<double, 2>>' is deprecated because it has a user-declared copy assignment operator [-Werror,-Wdeprecated-copy]
  operator=(const VectorizedArrayIterator<T> &other) = default;
  ^
/Applications/Xcode_14.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk/usr/include/c++/v1/__algorithm/copy_n.h:65:48: note: in implicit copy constructor for 'dealii::VectorizedArrayIterator<dealii::VectorizedArray<double, 2>>' first required here
    return _VSTD::copy(__first, __first + __n, __result);
                                               ^
/Users/runner/work/dealii/dealii/include/deal.II/base/vectorization.h:280:10: note: in instantiation of function template specialization 'std::copy_n<const double *, unsigned int, dealii::VectorizedArrayIterator<dealii::VectorizedArray<double, 2>>>' requested here
    std::copy_n(list.begin(), n_initializers, this->begin());
         ^
/Users/runner/work/dealii/dealii/include/deal.II/base/tensor.h:459:16: note: in instantiation of function template specialization 'dealii::VectorizedArray<double, 2>::VectorizedArray<double>' requested here
        return {{array[0], array[1]}};
               ^
/Users/runner/work/dealii/dealii/include/deal.II/base/tensor.h:1892:41: note: in instantiation of function template specialization 'dealii::internal::TensorImplementation::to_vectorized_array<2UL, double>' requested here
        internal::TensorImplementation::to_vectorized_array(values) * f);
                                        ^
/Users/runner/work/dealii/dealii/include/deal.II/base/geometry_info.h:3097:15: note: in instantiation of function template specialization 'dealii::Tensor<1, 2>::operator*=<double>' requested here
        point *= 2.0;
              ^