Merge branch 'fix/test_mpfa2p-failed-with-clang' into 'master'

Resolve "test_mpfa2p.cc broken with Clang 12"

Closes #1029

See merge request !2606
6 jobs for master in 0 seconds (queued for 68 minutes and 19 seconds)
Status Name Job ID Coverage
  Trigger
passed full-dune-2.7-clang

passed full-dune-2.7-gcc

passed full-dune-master-clang

passed full-dune-master-gcc

passed minimal-dune-2.7-gcc

 
  Downstream Modules
passed trigger lecture