Adjust test mute #119191 (#119206)

Author: martijnvg

muted-tests.yml

@@ -306,6 +306,7 @@ tests:
   method: testFailureLoadingFields
   issue: https://github.com/elastic/elasticsearch/issues/118000
 - class: org.elasticsearch.smoketest.SmokeTestMultiNodeClientYamlTestSuiteIT
+  method: test {yaml=indices.create/20_synthetic_source/create index with use_synthetic_source}
   issue: https://github.com/elastic/elasticsearch/issues/119191
 
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