ci(spanner): Fix nightly samples job failure for creating managed autoscalar instance (googleapis#3627)

Author: sakthivelmanii

samples/snippets/src/main/java/com/example/spanner/CreateInstanceWithAutoscalingConfigExample.java

@@ -24,6 +24,7 @@
 import com.google.spanner.admin.instance.v1.AutoscalingConfig;
 import com.google.spanner.admin.instance.v1.CreateInstanceRequest;
 import com.google.spanner.admin.instance.v1.Instance;
+import com.google.spanner.admin.instance.v1.Instance.Edition;
 import com.google.spanner.admin.instance.v1.InstanceConfigName;
 import com.google.spanner.admin.instance.v1.ProjectName;
 import java.util.concurrent.ExecutionException;
@@ -66,6 +67,7 @@ static void createInstance(String projectId, String instanceId) {
               .setDisplayName(displayName)
               .setConfig(
                   InstanceConfigName.of(projectId, configId).toString())
+              .setEdition(Edition.ENTERPRISE)
               .build();
 
       // Creates a new instance