Here's how you get it:
Breed 2 villagers and get only the baby.
Let the baby grow into an adult.
Have it zombified.
Push a minecart to it. The zombie villager won't ride at all. For some reason, zombie villagers from spawn eggs are able to ride minecarts just fine.
Thank you for your report!
We're tracking this issue in MCPE-76831, so this ticket is being resolved and linked as a duplicate.
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