webcomponents regression after 221

### Describe the bug

Web components with slots are broken after 221.



### Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-u4ec3o?embed=1&file=src%2Froutes%2F%2Bpage.svelte
The above repro is 221. update it then you can see that it breaks

### Logs

_No response_

### System Info

```shell
stackblitz
```


### Severity

blocking an upgrade