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

Merge branch 'feature/petsc-openmp' into 'master'

ref:dune-fem/dune-fem PETSc seems not to handle this internally.

See merge request [!292]

  [!292]: gitlab.dune-project.org/dune-fem/dune-fem/merge_requests/292
8 jobs from master in 69 minutes and 18 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #77290
stuttgart
debian-10-gcc-7-14

00:38:14

passed #77294
stuttgart
debian-10-gcc-7-14-nopetsc

00:37:00

passed #77291
stuttgart
debian-10-gcc-8-17

00:39:31

passed #77295
stuttgart
debian-10-gcc-8-17-petsc

01:08:40

passed #77292
stuttgart
debian-10-gcc-8-noassert-17

00:39:19

passed #77296
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debian-10-gcc-8-noassert-17-nopetsc

01:09:15

passed #77289
stuttgart
debian-9-gcc-6-14

00:34:40

passed #77293
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ubuntu-18.04-clang-6-17

00:35:49