Change shard changes api's threadpool from get to search (#34421)

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/ShardChangesAction.java

@@ -288,7 +288,7 @@ public class ShardChangesAction extends Action<ShardChangesAction.Response> {
                                IndexNameExpressionResolver indexNameExpressionResolver,
                                IndicesService indicesService) {
             super(settings, NAME, threadPool, clusterService, transportService, actionFilters,
-                    indexNameExpressionResolver, Request::new, ThreadPool.Names.GET);
+                    indexNameExpressionResolver, Request::new, ThreadPool.Names.SEARCH);
             this.indicesService = indicesService;
         }