[data-connect] Error property is missing in ExecuteGraphqlResponse

* Firebase Admin version: 13.5.0
* Firebase Product: data-connect
* Node.js version: 22

The `error` property is missing in the `ExecuteGraphqlResponse` interface

const result = await dataConnect.insert("TableName", Variables);

`result.errors` is not available despite the documentation stating it should be present [here](https://firebase.google.com/docs/reference/data-connect/rest/v1beta/GraphqlResponse)