Fix array builder append value to grow array only when needed.

Author: aardvark179

src/main/java/org/truffleruby/core/array/ArrayBuilderNode.java

@@ -198,7 +198,13 @@ public Object appendNewStrategy(Object store, int index, Object value) {
             final ArrayStrategy valueStrategy = ArrayStrategy.forValue(value);
             final ArrayStrategy generalized = currentStrategy.generalize(valueStrategy);
 
-            final int neededCapacity = ArrayUtils.capacityForOneMore(context, currentStrategy.capacityNode().execute(store));
+            int currentCapacity = currentStrategy.capacityNode().execute(store);
+            final int neededCapacity;
+            if (index >= currentCapacity) {
+                neededCapacity = ArrayUtils.capacityForOneMore(context, currentCapacity);
+            } else {
+                neededCapacity = currentCapacity;
+            }
 
             replaceNodes(generalized, neededCapacity);