chore(deps): update dependency tsdown to v0.21.6

Author: renovate[bot]

package.json

@@ -83,7 +83,7 @@
 		"prettier": "3.8.1",
 		"publint": "0.3.18",
 		"semantic-release": "25.0.3",
-		"tsdown": "0.21.5",
+		"tsdown": "0.21.6",
 		"typescript": "5.9.3",
 		"typescript-eslint": "^8.56.0",
 		"vitest": "3.2.4"