Bump external/spdlog from 91807c2 to ddce421

Bumps [external/spdlog](https://github.com/gabime/spdlog) from `91807c2` to `ddce421`.
- [Release notes](https://github.com/gabime/spdlog/releases)
- [Commits](gabime/spdlog@91807c2...ddce421)

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

Signed-off-by: dependabot[bot] <[email protected]>