fix: content gen error

Author: xaviergoh-bytedance

volcengine-java-sdk-ark-runtime/src/main/java/com/volcengine/ark/runtime/model/content/generation/GetContentGenerationTaskResponse.java

@@ -57,6 +57,14 @@ public void setStatus(String status) {
         this.status = status;
     }
 
+    public ContentGenerationError getError() {
+        return error;
+    }
+
+    public void setError(ContentGenerationError error) {
+        this.error = error;
+    }
+
     public Content getContent() {
         return content;
     }