Bump rand in /backend in the cargo group across 1 directory

Bumps the cargo group with 1 update in the /backend directory: [rand](https://github.com/rust-random/rand).


Updates `rand` from 0.9.2 to 0.9.3
- [Release notes](https://github.com/rust-random/rand/releases)
- [Changelog](https://github.com/rust-random/rand/blob/0.9.3/CHANGELOG.md)
- [Commits](rust-random/rand@rand_core-0.9.2...0.9.3)

---
updated-dependencies:
- dependency-name: rand
  dependency-version: 0.9.3
  dependency-type: direct:production
  dependency-group: cargo
...

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

Author: dependabot[bot]