Unmute SyntheticSourceRollingUpgradeIT (#133955)

The test requires that offsets are stored for leaf arrays.
Otherwise, arrays with single slot get synthesized as scalar fields.

Closes #133060
Closes #133061

Author: martijnvg

muted-tests.yml

@@ -456,12 +456,6 @@ tests:
 - class: org.elasticsearch.xpack.search.AsyncSearchErrorTraceIT
   method: testAsyncSearchFailingQueryErrorTraceDefault
   issue: https://github.com/elastic/elasticsearch/issues/133010
-- class: org.elasticsearch.upgrades.SyntheticSourceRollingUpgradeIT
-  method: testIndexing {upgradedNodes=1}
-  issue: https://github.com/elastic/elasticsearch/issues/133060
-- class: org.elasticsearch.upgrades.SyntheticSourceRollingUpgradeIT
-  method: testIndexing {upgradedNodes=0}
-  issue: https://github.com/elastic/elasticsearch/issues/133061
 - class: org.elasticsearch.xpack.ml.integration.TextEmbeddingQueryIT
   method: testModelWithPrefixStrings
   issue: https://github.com/elastic/elasticsearch/issues/133138

x-pack/plugin/logsdb/qa/rolling-upgrade/src/javaRestTest/java/org/elasticsearch/upgrades/SyntheticSourceRollingUpgradeIT.java

@@ -71,6 +71,7 @@ public SyntheticSourceRollingUpgradeIT(@Name("upgradedNodes") int upgradedNodes)
     }
 
     public void testIndexing() throws Exception {
+        assumeTrue("requires storing leaf array offsets", oldClusterHasFeature("gte_v9.1.0"));
         String dataStreamName = "logs-bwc-test";
         if (isOldCluster()) {
             startTrial();