Merge branch 'fix/dune-add-test-cmake-guard-skip-test' into 'master'

Timo Kochrequested to merge
tkoch/dune-common:cherry-pick-b7c41305 into releases/2.6

[cmake][dune_add_test] Fix/dune add test cmake guard skip test

See merge request !409 (merged) (cherry picked from commit b7c41305)

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