[Bug]: website: starlight ToC clip the page footer

### Describe the bug

On the release notes (and maybe also the docs pages), if the table of contents is long it hides under the footer at the bottom of the page:

### Reproduction

https://typespec.io/release-notes/typespec-1-12-0/

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
- [x] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/Microsoft/typespec/discussions).
- [x] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.