chore: bump tsdown from 0.21.8 to 0.21.9

Bumps [tsdown](https://github.com/rolldown/tsdown) from 0.21.8 to 0.21.9.
- [Release notes](https://github.com/rolldown/tsdown/releases)
- [Commits](rolldown/tsdown@v0.21.8...v0.21.9)

---
updated-dependencies:
- dependency-name: tsdown
  dependency-version: 0.21.9
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

package.json

@@ -5,7 +5,7 @@
         "@apst/tsconfig": "~0.3.0",
         "@apst/tsdown": "~0.3.0",
         "@biomejs/biome": "^2.4.12",
-        "tsdown": "~0.21.8",
+        "tsdown": "~0.21.9",
         "typedoc": "~0.28.19",
         "typedoc-plugin-markdown": "^4.11.0",
         "typescript": "^6.0.2"