Mark list as frozen and shareable

encoding.c

@@ -152,6 +152,8 @@ enc_list_update(int index, rb_raw_encoding *encoding)
         RBASIC_CLEAR_CLASS(new_list);
         /* initialize encoding data */
         rb_ary_store(new_list, index, enc_new(encoding));
+        rb_ary_freeze(new_list);
+        FL_SET_RAW(new_list, RUBY_FL_SHAREABLE);
         RUBY_ATOMIC_VALUE_SET(rb_encoding_list, new_list);
     }
 }