Mute UpgradeClusterClientYamlTestSuiteIT."Test old cluster datafeed without aggs"

Signed-off-by: Mark Vieira <portugee@gmail.com>

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/mixed_cluster/40_ml_datafeed_crud.yml

@@ -8,6 +8,9 @@ setup:
 
 ---
 "Test old cluster datafeed without aggs":
+  - skip:
+      version: "all"
+      reason: "Awaits fix: https://github.com/elastic/elasticsearch/issues/52739"
   - do:
       ml.get_datafeeds:
         datafeed_id: old-cluster-datafeed-without-aggs