Fix generation of constrained shapes reaching `@sensitive` shapes (#2585)

Constrained shapes should always be able to `#[derive(Debug)]`.

Fixes #2582.

## Testing

The modified integration test fails without this patch applied.

## Checklist
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- [x] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates

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Co-authored-by: Matteo Bigoi <1781140+crisidev@users.noreply.github.com>