Website does not build: Missing MPI for building sphinx documentation of dune-testtools

At the moment the website does not build. For me it looks like there is an issue with building the sphinx documentation of dune-testtools and missing MPI in the ci-website-buildet docker image.

I will try adding mpi to

https://gitlab.dune-project.org/infrastructure/ci-website-builder/-/blob/master/install.sh

and see if that helps.