fix(securitycenter): update filter field to mutable path (GoogleCloudPlatform#1115)

Author: hannah-tsai

securitycenter/src/update_notification.php

@@ -42,7 +42,7 @@
 $notificationConfigName = $securityCenterClient::notificationConfigName($organizationId, $notificationConfigId);
 
 $streamingConfig = (new StreamingConfig())->setFilter("state = \"ACTIVE\"");
-$fieldMask = (new FieldMask())->setPaths(['description', 'pubsub_topic']);
+$fieldMask = (new FieldMask())->setPaths(['description', 'pubsub_topic', 'streaming_config.filter']);
 $notificationConfig = (new NotificationConfig())
     ->setName($notificationConfigName)
     ->setDescription('Updated description.')