create-pull-request action fails on delete

### TL;DR

I believe this is caused by the [loop](https://github.com/abcxyz/actions/blob/2c7fac9c570b3c4e27cda7b08bcb143787391eed/.github/actions/create-pull-request/action.yml#L299) that iterates over deleted files and attempts to get the file's mode via the `stat` command. Unfortunately, one cannot stat a deleted file.

My first idea to fix is to see if we need a file's mode for deleted files. I'm hoping we don't, so similar to the SHA, we can just leave it unset/null.

### Expected behavior

_No response_

### Observed behavior

Unhandled error: Error: ENOENT: no such file or directory, stat ''

### Environment Details

```markdown
N/A
```

### Additional information

_No response_