Mute org.elasticsearch.upgrades.SyntheticSourceRollingUpgradeIT testIndexing {upgradedNodes=2} #135344

muted-tests.yml

@@ -660,6 +660,9 @@ tests:
 - class: org.elasticsearch.upgrades.TextRollingUpgradeIT
   method: testIndexing {upgradedNodes=1}
   issue: https://github.com/elastic/elasticsearch/issues/135236
+- class: org.elasticsearch.upgrades.SyntheticSourceRollingUpgradeIT
+  method: testIndexing {upgradedNodes=2}
+  issue: https://github.com/elastic/elasticsearch/issues/135344
 
 # Examples:
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