Attribute Modifiers don't work on horse armor anymore

Applying a generic.armor attribute when worn on  the body for a horse armor doesn't provide any protection to the horse. This worked on 1.20.4.

 
To reproduce:

1. Add the following loot table to a datapack in your world.
 

{    "pools": [        {            "rolls": 1,            "entries": [                {                    "type": "item",                    "name": "leather_horse_armor",                    "functions": [                        {                          "function": "minecraft:set_attributes",                          "modifiers": [                            {                              "attribute": "minecraft:generic.armor",                              "name": "",                              "amount": 20,                              "operation": "add_value",                              "slot": "chest"                            }                          ]                        }                    ]                }            ]        }    ]}

2. Give it to yourself via /loot give @s loot <namespace:loottable>

3. Equip it to your horse. Check the max HP it has.
4. Hit it with a diamond pickaxe.
5. Chack its max HP again. It will have decreased by 5HP points, omitting all and any protection.