Zombie kills Villager during Conversion on Hard Difficulty

Summary:
Instead of being zombified, villagers die from zombie attacks even on hard difficulty.

Steps to Reproduce:
1. Build a confinement space for testing.
2. Set /difficulty to hard.
2. Summon (1) villager and (1) zombie within confinement.
3. Wait for the zombie to attempt to infect villager.

Observed Results:
Villager dies after ~6 attacks from the zombie.

Expected Results:
On hard difficulty, villager conversion to zombie villager is 100%