Assert only primitive arrays are seen by the default implementation.

Author: aardvark179

src/main/java/org/truffleruby/core/array/library/ArrayStoreLibrary.java

@@ -129,6 +129,7 @@ public Object makeShared(Object store) {
     /** Do any work required to start sharing elements across threads in the range from {@code start} (inclusive) to
      * {@code end} (exclusive). */
     public void shareElements(Object store, int start, int end) {
+        assert isPrimitive(store);
     }
 
     /** Return a description of {@code store} for debugging output. */