[bugfix][Petsc] Guard operations to matrix with omp critical. Petsc

cannot handle this internally.
4 jobs for feature/petsc-openmp in 42 minutes and 58 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #77007
stuttgart
debian-10-gcc-7-14

00:28:40

passed #77009
stuttgart
debian-10-gcc-7-14-nopetsc

00:26:58

passed #77006
stuttgart
debian-9-gcc-6-14

00:39:55

passed #77008
stuttgart
ubuntu-18.04-clang-6-17

00:42:58