SPIGOT-6831: Fix llama strength crash

By: md_5 <git@md-5.net>

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftLlama.java

@@ -47,7 +47,7 @@ public class CraftLlama extends CraftChestedHorse implements Llama {
     public void setStrength(int strength) {
         Preconditions.checkArgument(1 <= strength && strength <= 5, "strength must be [1,5]");
         if (strength == getStrength()) return;
-        getHandle().setStrength(strength);
+        getHandle().setStrengthPublic(strength);
         getHandle().createInventory();
     }