If a villager/wandering trader is spawned riding a zombie/husk, they will be immune to its attacks but they continue to be targeted by the zombie.

Command: /summon minecraft:zombie ~ ~ ~ {Passengers:[

]}

This causes the zombie/husk to walk around in circles, and they refuse to attack other villagers even if they are placed in the same block.

Note: This does not happen with other creatures of similar nature (e.g. a chicken riding an ocelot or a hostile mob riding an iron golem).