[1.21.8] Can't set horse armor

`/npc property set <horse-npc> chestplate` does nothing on 1.21.8. Found solution:
```diff
if (EntityTypes.isTypeInstanceOf(type, EntityTypes.HORSE)) {
-    addProperties("chestplate");
+    addProperties("body");
}
```

But I didn't create a PR because I don't want to manually search in which mc version it changed. Maybe I will do it later 

("supporting 1.8 to latest" makes things hard)