make sure AggregationTest creates reduced aggregations. (#63931)

The test calls InternalAggregationTestCase#createTestInstanceForXContent() instead of InternalAggregationTestCase#createTestInstance() (The method needs to become public)

server/src/test/java/org/elasticsearch/search/aggregations/AggregationsTests.java

@@ -296,7 +296,7 @@ public class AggregationsTests extends ESTestCase {
                     singleBucketAggTestCase.subAggregationsSupplier = () -> InternalAggregations.EMPTY;
                 }
             }
-            aggs.add(testCase.createTestInstance());
+            aggs.add(testCase.createTestInstanceForXContent());
         }
         return InternalAggregations.from(aggs);
     }

server/src/test/java/org/elasticsearch/search/aggregations/metrics/InternalScriptedMetricTests.java

@@ -160,7 +160,7 @@ public class InternalScriptedMetricTests extends InternalAggregationTestCase<Int
     }
 
     @Override
-    protected InternalScriptedMetric createTestInstanceForXContent() {
+    public InternalScriptedMetric createTestInstanceForXContent() {
         InternalScriptedMetric aggregation = createTestInstance();
         return (InternalScriptedMetric) aggregation.reduce(
             singletonList(aggregation),

test/framework/src/main/java/org/elasticsearch/test/InternalAggregationTestCase.java

@@ -436,7 +436,7 @@ public abstract class InternalAggregationTestCase<T extends InternalAggregation>
         return createUnmappedInstance(name, metadata);
     }
 
-    protected T createTestInstanceForXContent() {
+    public T createTestInstanceForXContent() {
         return createTestInstance();
     }