build(deps): Bump external/fmt from 5676e40 to d42a068

Bumps [external/fmt](https://github.com/fmtlib/fmt) from `5676e40` to `d42a068`.
- [Release notes](https://github.com/fmtlib/fmt/releases)
- [Commits](fmtlib/fmt@5676e40...d42a068)

---
updated-dependencies:
- dependency-name: external/fmt
  dependency-type: direct:production
...

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