/usr/include/osgShadow/ is in libopenscenegraph-dev 3.2.1-6.
This file is owned by root:root, with mode 0o755.
..
/usr/include/osgShadow/ConvexPolyhedron
/usr/include/osgShadow/DebugShadowMap
/usr/include/osgShadow/Export
/usr/include/osgShadow/LightSpacePerspectiveShadowMap
/usr/include/osgShadow/MinimalCullBoundsShadowMap
/usr/include/osgShadow/MinimalDrawBoundsShadowMap
/usr/include/osgShadow/MinimalShadowMap
/usr/include/osgShadow/OccluderGeometry
/usr/include/osgShadow/ParallelSplitShadowMap
/usr/include/osgShadow/ProjectionShadowMap
/usr/include/osgShadow/ShadowMap
/usr/include/osgShadow/ShadowSettings
/usr/include/osgShadow/ShadowTechnique
/usr/include/osgShadow/ShadowTexture
/usr/include/osgShadow/ShadowVolume
/usr/include/osgShadow/ShadowedScene
/usr/include/osgShadow/SoftShadowMap
/usr/include/osgShadow/StandardShadowMap
/usr/include/osgShadow/Version
/usr/include/osgShadow/ViewDependentShadowMap
/usr/include/osgShadow/ViewDependentShadowTechnique