Enable S3 Express canary by default (#3499)

## Motivation and Context
Now that canary [passed for the last three
days](https://github.com/awslabs/aws-sdk-rust/actions/runs/8335320052),
we can turn s3 express canary on by default.

## Testing
Verified internally that our release pipeline passes canary with s3
express canary enabled.

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._