COMP: Clang Tidy-Fix modernize-use-override at itkTestOutputWindow.h
COMP: Clang Tidy-Fix modernize-use-override at itkTestOutputWindow.h

Follow-up to elastix issue #110 ("-Winconsistent-missing-override on MacOS") by Harmen Stoppels

SuperElastix/elastix,SuperElastix/elastix,SuperElastix/elastix,SuperElastix/elastix,SuperElastix/elastix