Update NetCDF to 4.9.1 for UBSan fixes
Building VTK with UBSan results in many test failures. Most that remain at this point are actually due to bugs in NetCDF. I have fixed at least some of them upstream. So now I'd like to get NetCDF in VTK updated to 4.9.1 (current release).
@ben.boeckel could you help me again with how to get NetCDF 4.9.1 into the kitware fork at https://gitlab.kitware.com/third-party/netcdf.git ? That is the first step, right?