When a wolf is near a Wither Skeleton, the Wither Skeleton does not flee from the wolf. The Wither Skeleton continues to randomly wander the area as if the wolf isn't there.
I've tried it in both Creative and Survival on Hard difficulty. The Wither Skeleton ignores the wolf.
Can confirm in 1.21.130. This is because the Wither Skeleton is completely missing the behaviour.avoid_mob_type component in its .json file. Since its already in the skeletons .json file, fixing it is as simple as pasting the code from the skeletons .json file.