ESQL: Clean index when retrying test (elastic#121954)

This modifies the `HeapAttackIT` test to clean an index created by the
test if we have to retry it.

Closes elastic#121873

Author: nik9000

test/external-modules/esql-heap-attack/src/javaRestTest/java/org/elasticsearch/xpack/esql/heap_attack/HeapAttackIT.java

@@ -684,6 +684,7 @@ private Map<String, Object> lookupExplosion(int sensorDataCount, int lookupEntri
             return responseAsMap(query(query.toString(), null));
         } finally {
             deleteIndex("sensor_data");
+            deleteIndex("sensor_lookup");
         }
     }