Bump svelte from 3.42.6 to 3.49.0 in /demo

Bumps [svelte](https://github.com/sveltejs/svelte) from 3.42.6 to 3.49.0.
- [Release notes](https://github.com/sveltejs/svelte/releases)
- [Changelog](https://github.com/sveltejs/svelte/blob/master/CHANGELOG.md)
- [Commits](sveltejs/svelte@v3.42.6...v3.49.0)

---
updated-dependencies:
- dependency-name: svelte
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>