Summary:
Discovered while testing MC-269304. The armor.body slot can have horse armor, wolf armor and carpets on horses, wolves and llamas. The problem is that all of these items protect the wolf from damage. Only the wolf armor has durability, so non-wolf armor items can protect the wolf forever.

Steps to reproduce:

1. Tame a wolf

2. /item replace entity @e[type=minecraft:wolf,limit=1] armor.body with minecraft:leather_horse_armor

3. Hit the wolf

4. /data get entity @e[type=minecraft:wolf,limit=1,sort=nearest] Health

5. /item replace entity @e[type=minecraft:wolf,limit=1,sort=nearest] armor.body with minecraft:white_carpet

6. Hit the wolf

   /data get entity @e[type=minecraft:wolf,limit=1,sort=nearest] Health

Observed results:
The horse armor and carpet protected the wolf from the damage. This can be noticed by hearing the sound when the wolf takes damage as well as by the /data command telling you that the wolf has full health.

Expected results:
Only wolf armor should protect wolves from damage, not horse armor and carpets.

Screenshots: