cargo(deps): update rand requirement from 0.8.5 to 0.9.2 in /rustmail

Updates the requirements on [rand](https://github.com/rust-random/rand) to permit the latest version.
- [Release notes](https://github.com/rust-random/rand/releases)
- [Changelog](https://github.com/rust-random/rand/blob/master/CHANGELOG.md)
- [Commits](rust-random/rand@0.8.5...rand_core-0.9.2)

---
updated-dependencies:
- dependency-name: rand
  dependency-version: 0.9.2
  dependency-type: direct:production
...

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

Author: dependabot[bot]

rustmail/Cargo.toml

@@ -22,7 +22,7 @@ rust-embed = "8.7.2"
 mime_guess = "2.0.5"
 urlencoding = "2.1.3"
 serde_json = "1.0.145"
-rand = "0.8.5"
+rand = "0.9.2"
 base64 = "0.22.1"
 subtle = "2.6.1"