Use List#of method in Autoscaling#getActions

This commit replaces a use of Collections#emptyList with List#of as the
preferred approach for collection convenience methods in master.

x-pack/plugin/autoscaling/src/main/java/org/elasticsearch/xpack/autoscaling/Autoscaling.java

@@ -24,7 +24,6 @@
 import org.elasticsearch.xpack.autoscaling.action.TransportGetAutoscalingDecisionAction;
 import org.elasticsearch.xpack.autoscaling.rest.RestGetAutoscalingDecisionHandler;
 
-import java.util.Collections;
 import java.util.List;
 import java.util.function.Supplier;
 
@@ -64,7 +63,7 @@ public List<Setting<?>> getSettings() {
         if (enabled) {
             return List.of(new ActionHandler<>(GetAutoscalingDecisionAction.INSTANCE, TransportGetAutoscalingDecisionAction.class));
         } else {
-            return Collections.emptyList();
+            return List.of();
         }
     }