[md][stokesdarcy] adapt reference solutions

After rebasing, the tests failed due to 0ccde397
that had been introduced on master.
Status Name Job ID Coverage
  Trigger
manual full-dune-2.7-clang
manual full-dune-2.7-gcc
manual full-dune-master-gcc
manual minimal-dune-2.7-gcc
 
  Downstream Modules
created trigger lecture