Bump tsdown from 0.19.0 to 0.20.1

Bumps [tsdown](https://github.com/rolldown/tsdown) from 0.19.0 to 0.20.1.
- [Release notes](https://github.com/rolldown/tsdown/releases)
- [Commits](rolldown/tsdown@v0.19.0...v0.20.1)

---
updated-dependencies:
- dependency-name: tsdown
  dependency-version: 0.20.1
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]