Fix compile error

Signed-off-by: Lantao Jin <ltjin@amazon.com>

Author: LantaoJin

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalciteMvCombineCommandIT.java

@@ -232,10 +232,10 @@ private static List<String> toStringListKeepNulls(Object cell) {
     if (cell == null || cell == JSONObject.NULL) {
       return Collections.emptyList();
     }
-    if (cell instanceof JSONArray arr) {
+    if (cell instanceof JSONArray) {
       List<String> out = new ArrayList<>();
-      for (int i = 0; i < arr.length(); i++) {
-        Object v = arr.get(i);
+      for (int i = 0; i < ((JSONArray) cell).length(); i++) {
+        Object v = ((JSONArray) cell).get(i);
         out.add(v == JSONObject.NULL ? null : String.valueOf(v));
       }
       return out;