fix: use Integer.class for SELECT VALUE COUNT aggregate serializer test

SELECT VALUE COUNT(1) returns a scalar integer, so use Integer.class
instead of ObjectNode.class as the result type. ObjectNode.class fails
because ValueUnwrapCosmosItemSerializer extracts the _value field and
cannot convert the resulting integer to ObjectNode.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: xinlian12

sdk/cosmos/azure-cosmos-tests/src/test/java/com/azure/cosmos/CosmosItemSerializerTest.java

@@ -764,18 +764,20 @@ public void queryWithAggregateAndCustomSerializer() {
             // results (e.g., COUNT) are not full documents and cannot be deserialized
             // by the envelope-wrapping serializer. The test still validates that the
             // client-level custom serializer does not leak into the internal query pipeline.
+            // SELECT VALUE COUNT(1) returns a scalar integer, so use Integer.class.
             CosmosQueryRequestOptions queryRequestOptions = new CosmosQueryRequestOptions()
                 .setCustomItemSerializer(CosmosItemSerializer.DEFAULT_SERIALIZER);
 
-            List<ObjectNode> results = container
+            List<Integer> results = container
                 .queryItems(
                     "SELECT VALUE COUNT(1) FROM c WHERE c.mypk = '" + pkValue + "'",
                     queryRequestOptions,
-                    ObjectNode.class)
+                    Integer.class)
                 .stream().collect(Collectors.toList());
 
             assertThat(results).isNotNull();
             assertThat(results).hasSize(1);
+            assertThat(results.get(0)).isEqualTo(3);
         } finally {
             for (String id : createdIds) {
                 try {