Bump external/spdlog from 6230201 to 8fed530 (#1534)

Bumps [external/spdlog](https://github.com/gabime/spdlog) from `6230201` to `8fed530`.
- [Release notes](https://github.com/gabime/spdlog/releases)
- [Commits](gabime/spdlog@6230201...8fed530)

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

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