Closing the directory reader to fix test (opensearch-project#17968)

Signed-off-by: expani <[email protected]>
Signed-off-by: Harsh Kothari <[email protected]>

Author: expani

server/src/test/java/org/opensearch/search/aggregations/startree/RangeAggregatorTests.java

@@ -174,6 +174,7 @@ public void testRangeAggregation() throws IOException {
             }
         }
 
+        ir.close();
         reader.close();
         directory.close();
     }