Merged requested to merge cleanup/reduce_doxyerr into master
What this MR does / why does DuMux need it:
This MR reduces the error file
buildfolder/doc/doxygen/doxyerr.log to include only error that are present (and unsolvable) since several releases.
Related to #1178 (closed)
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do the test pipelines pass? (see guide on how to run pipelines for a merge request)
non-applicable points in this list deleted