Issue: Error when using safe_output.push_to_pull_request_branch

I’m encountering an error whenever I try to use safe_output.push_to_pull_request_branch:

```
push_to_pull_request_branch
└ {"result":"error","error":"Cannot generate incremental patch: failed to fetch..."}
```

I’m not sure whether this is a bug or if I’m missing some configuration. Could you please take a look?

### Steps to Reproduce

Set up a workflow that is automatically triggered on CI when a pull request is opened or synchronized against the default branch (e.g., main), with path filters applied.

Configure the workflow similar to the following:

```
safe-outputs:
github-app:
app-id: ${{ vars.APP_ID }}
private-key: ${{ secrets.APP_PRIVATE_KEY }}
push-to-pull-request-branch:
max: 3
```

Define and run the Agentic Workflow that attempts to push changes back to the pull request branch.

### Observed Behavior

The workflow fails with:

Cannot generate incremental patch: failed to fetch...
Expected Behavior

The action should successfully generate and push incremental changes to the pull request branch.