PR Preview redeploying the connected backend

### Before opening, please confirm:

- [X] I have checked to see if my question is addressed in the [FAQ](https://github.com/aws-amplify/amplify-hosting/blob/master/FAQ.md).
- [X] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-hosting/issues?q=is%3Aissue+).
- [X] I have read the guide for [submitting bug reports](https://github.com/aws-amplify/amplify-hosting/blob/master/CONTRIBUTING.md).
- [X] I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.
- [X] I have removed any sensitive information from my code snippets and submission.

### App Id

d1vnnqyaojjytn

### AWS Region

us-east-1

### Amplify Hosting feature

Backend builds

### Describe the bug

PR preview is re-deploying the backend which eventually throwing a error.

### Expected behavior

If PR preview is connected to existing backend then it should to pull only. while connected branch build is working fine.

### Reproduction steps

A PR is with error is there in provided app id to reproduce.

### Build Settings

```yaml
There's no specific setting.
```

### Log output

```
# Put your logs below this line

Resource is not in the state stackUpdateComplete
Name: S3Bucket (AWS::S3::Bucket), Event Type: create, Reason: xxxxxxx-prod already exists
Session Identifier: 68c46c78-468c-4b62-988b-a4cb173a65a7
```

### Additional information

_No response_

Start by reproducing the PR preview backend build for app d1vnnqyaojjytn in us-east-1 and review the build log showing the stackUpdateComplete and existing S3Bucket errors. Trace why the connected backend is redeployed instead of pulled; done means PR previews use the existing backend without attempting to create the already-existing bucket.

Written by the indexing model from the issue text.