Bump external/fmt from 86e27cc to 7e4ad40

Bumps [external/fmt](https://github.com/fmtlib/fmt) from `86e27cc` to `7e4ad40`.
- [Release notes](https://github.com/fmtlib/fmt/releases)
- [Commits](fmtlib/fmt@86e27cc...7e4ad40)

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

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