Mute org.elasticsearch.xpack.ml.integration.ClassificationIT testSetUpgradeMode_ExistingTaskGetsUnassigned elastic#121928

Author: elasticsearchmachine

muted-tests.yml

@@ -557,3 +557,6 @@ tests:
   issue: https://github.com/elastic/elasticsearch/issues/121680
 - class: org.elasticsearch.xpack.migrate.action.ReindexDatastreamIndexTransportActionIT
   issue: https://github.com/elastic/elasticsearch/issues/121737
+- class: org.elasticsearch.xpack.ml.integration.ClassificationIT
+  method: testSetUpgradeMode_ExistingTaskGetsUnassigned
+  issue: https://github.com/elastic/elasticsearch/issues/121928