ec2: change marked as alpha in release notes

### Describe the issue

Why is https://github.com/aws/aws-cdk/issues/34618 listed in alpha section of [v2.203.0 release](https://github.com/aws/aws-cdk/releases/tag/v2.203.0)? Shouldn't that be in the standard section?

### Links

-