ES|QL: Unmute generative tests (elastic#134888)

Related to: elastic#134407

The only relevant failures are the same as
elastic#133794, but since it was
closed yesterday, I'll give it another try.

If it still fails, I'll reopen the issue and I'll add `Connection is
closed` as a muted exception.

Author: luigidellaquila

muted-tests.yml

@@ -543,9 +543,6 @@ tests:
 - class: org.elasticsearch.discovery.DiscoveryDisruptionIT
   method: testElectMasterWithLatestVersion
   issue: https://github.com/elastic/elasticsearch/issues/134748
-- class: org.elasticsearch.xpack.esql.qa.single_node.GenerativeIT
-  method: test
-  issue: https://github.com/elastic/elasticsearch/issues/134407
 - class: org.elasticsearch.compute.lucene.TimeSeriesSourceOperatorTests
   method: testSliceIndex
   issue: https://github.com/elastic/elasticsearch/issues/134808