Scatterer from DOLFINx #3885 gives different results than prior implementation

[jorgensd]

Breaks distribute_ghost_data.
To be investigated.
Probably std::int8_t related. PR in question: FEniCS/dolfinx#3855
New code looks like:

    MPI_Request request = MPI_REQUEST_NULL;
    ghost_scatterer.scatter_fwd_begin(indicator.data(),
                                      recieve_indicator.data(), request);
    ghost_scatterer.scatter_end(request);

old code was

ghost_scatterer.scatter_fwd(std::span<const std::int8_t>(indicator),
                                std::span<std::int8_t>(recieve_indicator));