[test] Correctly mute MixedClusterClientYamlTestSuiteIT {cat.shards/10_basic/Help} (#116398)

The `sync_id` field was removed from the `cat shards` output for 9.0 in
#114246, this test shouldn't be run along with other 8.x clusters

Resolve #116110

Author: arteam

muted-tests.yml

@@ -87,9 +87,6 @@ tests:
   issue: https://github.com/elastic/elasticsearch/issues/115816
 - class: org.elasticsearch.xpack.application.connector.ConnectorIndexServiceTests
   issue: https://github.com/elastic/elasticsearch/issues/116087
-- class: org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT
-  method: test {p0=cat.shards/10_basic/Help}
-  issue: https://github.com/elastic/elasticsearch/issues/116110
 - class: org.elasticsearch.xpack.ml.integration.DatafeedJobsRestIT
   method: testLookbackWithIndicesOptions
   issue: https://github.com/elastic/elasticsearch/issues/116127

qa/mixed-cluster/build.gradle

@@ -67,6 +67,9 @@ excludeList.add('indices.resolve_index/20_resolve_system_index/*')
 // Excluded because the error has changed
 excludeList.add('aggregations/percentiles_hdr_metric/Negative values test')
 
+// sync_id is removed in 9.0
+excludeList.add("cat.shards/10_basic/Help")
+
 def clusterPath = getPath()
 
 buildParams.bwcVersions.withWireCompatible { bwcVersion, baseName ->