Merge branch 'features/shut-up-compiler-warnings' into 'master'

Get rid of unused/shadowed variable compiler warnings.

See merge request !442 (merged)

(cherry picked from commit b0a1b9c7)

b6080f4f Get rid of unused/shadowed variable compiler warnings. a43015f8 USe std::is_sorted to fix compile issue with DUNE_ISTL_WITH_CHECKING.

enabled an automatic merge when the pipeline for 0c4deb73 succeeds

mentioned in commit 468c9852

merged