Mute org.elasticsearch.upgrades.SyntheticSourceRollingUpgradeIT testIndexing {upgradedNodes=3} #135338

muted-tests.yml

@@ -645,6 +645,9 @@ tests:
 - class: org.elasticsearch.search.sort.FieldSortIT
   method: testSortMixedFieldTypes
   issue: https://github.com/elastic/elasticsearch/issues/129445
+- class: org.elasticsearch.upgrades.SyntheticSourceRollingUpgradeIT
+  method: testIndexing {upgradedNodes=3}
+  issue: https://github.com/elastic/elasticsearch/issues/135338
 
 # Examples:
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