Unmute multi_node generative tests

A partial mute was already put in place in
#131515 and the bot just
muted this after the fact for some reason.

Author: alex-spies

muted-tests.yml

@@ -467,9 +467,6 @@ tests:
 - class: org.elasticsearch.xpack.search.CrossClusterAsyncSearchIT
   method: testCancellationViaTimeoutWithAllowPartialResultsSetToFalse
   issue: https://github.com/elastic/elasticsearch/issues/131248
-- class: org.elasticsearch.xpack.esql.qa.multi_node.GenerativeIT
-  method: test
-  issue: https://github.com/elastic/elasticsearch/issues/131508
 - class: org.elasticsearch.action.admin.cluster.node.tasks.CancellableTasksIT
   method: testRemoveBanParentsOnDisconnect
   issue: https://github.com/elastic/elasticsearch/issues/131562