Reenable HeapAttackIT testHugeManyConcat() (#100511)

Reenable testHugeManyConcat().

x-pack/plugin/esql/qa/server/single-node/src/javaRestTest/java/org/elasticsearch/xpack/esql/qa/single_node/HeapAttackIT.java

@@ -192,7 +192,6 @@ public class HeapAttackIT extends ESRestTestCase {
     /**
      * Hits a circuit breaker by building many moderately long strings.
      */
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/99826")
     public void testHugeManyConcat() throws IOException {
         initManyLongs();
         assertCircuitBreaks(() -> manyConcat(2000));