Unmute testManyConcat (elastic#138508)

With elastic#138432 we split HeapAttackIT into two different test to avoid timeouts. With the change testManyConcat should not timeout sporadically any more.

Closes elastic#136728

Author: julian-elastic

muted-tests.yml

@@ -322,9 +322,6 @@ tests:
 - class: org.elasticsearch.test.rest.yaml.RcsCcsCommonYamlTestSuiteIT
   method: test {p0=search.vectors/200_dense_vector_docvalue_fields/Enable docvalue_fields parameter for dense_vector fields}
   issue: https://github.com/elastic/elasticsearch/issues/136443
-- class: org.elasticsearch.xpack.esql.heap_attack.HeapAttackIT
-  method: testManyConcat
-  issue: https://github.com/elastic/elasticsearch/issues/136728
 - class: org.elasticsearch.xpack.search.CrossClusterAsyncSearchIT
   method: testRemoteClusterOnlyCCSWithFailuresOnAllShards
   issue: https://github.com/elastic/elasticsearch/issues/136894