docs(custom-resource-handlers): fix typo (#32948)

### Issue # (if applicable)

None

### Reason for this change

Fixed typos in code comments.

### 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)

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