chore(deps): bump undici and @sveltejs/kit in /demos/svelte (#70)

Bumps [undici](https://github.com/nodejs/undici) to 5.26.3 and updates ancestor dependency [@sveltejs/kit](https://github.com/sveltejs/kit/tree/HEAD/packages/kit). These dependencies need to be updated together.


Updates `undici` from 5.20.0 to 5.26.3
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v5.20.0...v5.26.3)

Updates `@sveltejs/kit` from 1.15.2 to 1.26.0
- [Release notes](https://github.com/sveltejs/kit/releases)
- [Changelog](https://github.com/sveltejs/kit/blob/master/packages/kit/CHANGELOG.md)
- [Commits](https://github.com/sveltejs/kit/commits/@sveltejs/[email protected]/packages/kit)

---
updated-dependencies:
- dependency-name: undici
  dependency-type: indirect
- dependency-name: "@sveltejs/kit"
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>