Merge branch 'issue/remove_warning_problemstat' into 'master'

remove 'xyz is already created' warning in ProblemStat::initialize

See merge request !211
4 jobs for master in 68 minutes and 37 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #21182
dune-2.6

00:25:49

passed #21183
dune-2.7

00:33:48

passed #21184
dune-git

00:31:50

passed #21185
dune-git-full

00:42:47