build: update rand to 0.9

We already have both rand 0.8 and rand 0.9
in our dependency tree.

We still need rand 0.8 because
public APIs of rPGP 0.17.0 and Iroh 0.35.0
use rand 0.8 types in public APIs,
so it is imported as rand_old.

src/imex/key_transfer.rs

@@ -1,8 +1,6 @@
 //! # Key transfer via Autocrypt Setup Message.
 use std::io::BufReader;
 
-use rand::{Rng, thread_rng};
-
 use anyhow::{Result, bail, ensure};
 
 use crate::blob::BlobObject;
@@ -133,12 +131,11 @@ pub async fn render_setup_file(context: &Context, passphrase: &str) -> Result<St
 /// Creates a new setup code for Autocrypt Setup Message.
 fn create_setup_code(_context: &Context) -> String {
     let mut random_val: u16;
-    let mut rng = thread_rng();
     let mut ret = String::new();
 
     for i in 0..9 {
         loop {
-            random_val = rng.r#gen();
+            random_val = rand::random();
             if random_val as usize <= 60000 {
                 break;
             }