Bump rand from 0.8.3 to 0.8.4 in /fog/ledger/enclave/trusted

Bumps [rand](https://github.com/rust-random/rand) from 0.8.3 to 0.8.4.
- [Release notes](https://github.com/rust-random/rand/releases)
- [Changelog](https://github.com/rust-random/rand/blob/master/CHANGELOG.md)
- [Commits](rust-random/rand@0.8.3...0.8.4)

---
updated-dependencies:
- dependency-name: rand
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>