chore: fetch lfs files for sync-workflow (#33359)

### Issue # (if applicable)

Closes NA

### Reason for this change

Fetch LFS files from upstream

### Description of changes

The sync job is currently failing with the following error: while attempting to find the commit for LFS files, it is unable to locate them because these commits exist in the remote repository but are not part of the private repository.

Error
```
Unable to find source for object 08a8ab95e23c6a82be4d9be42ee1ba55cb493cc1bde73c25f8bb700447263cc6 
(try running `git lfs fetch --all`)
```

To resolve it added command `git lfs fetch upstream`

Failure logs: https://github.com/aws/aws-cdk-private/actions/runs/13232341293
Success test run after change: https://github.com/aws/aws-cdk-private/actions/runs/13234030490



### Describe any new or updated permissions being added

NA


### Description of how you validated changes

Successful test run for workflow with change in side branch : 
https://github.com/aws/aws-cdk-private/actions/runs/13234030490

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: shikha372

.github/workflows/sync-from-upstream.yml

@@ -63,6 +63,7 @@ jobs:
         run: |-
           git remote add upstream https://github.com/aws/aws-cdk.git
           git fetch upstream $BRANCHES
+          git lfs fetch upstream
 
           for branch in $BRANCHES; do
             git push origin --force refs/remotes/upstream/$branch:refs/heads/$branch