Add GenericLabelInterpolator classification_s4.mha (bafkreieknicyj6a22rizrcyfy4pzx5pskm4loi3m7h5gbi2qp2cc3ny3my)

Sibling blob to gl_gaussian_3.mha from ITK commit 195fdabc11 (downsized
RotateLabels test fixture); its content-link landed in ITK but the blob
was never mirrored, so clean checkouts fail ExternalData resolution.

Co-Authored-By: Bradley Lowekamp <blowekamp@mail.nih.gov>

Author: hjmjohnson