Build: Bump defu from 6.1.4 to 6.1.6

Bumps [defu](https://github.com/unjs/defu) from 6.1.4 to 6.1.6.
- [Release notes](https://github.com/unjs/defu/releases)
- [Changelog](https://github.com/unjs/defu/blob/main/CHANGELOG.md)
- [Commits](unjs/defu@v6.1.4...v6.1.6)

Closes gh-266

---
updated-dependencies:
- dependency-name: defu
  dependency-version: 6.1.6
  dependency-type: indirect
...

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