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/authres.rs

@@ -468,7 +468,7 @@ Authentication-Results: box.hispanilandia.net; spf=pass smtp.mailfrom=adbenitez@
             // The ordering in which the emails are received can matter;
             // the test _should_ pass for every ordering.
             dir.sort_by_key(|d| d.file_name());
-            //rand::seq::SliceRandom::shuffle(&mut dir[..], &mut rand::thread_rng());
+            //rand::seq::SliceRandom::shuffle(&mut dir[..], &mut rand::rng());
 
             for entry in &dir {
                 let mut file = fs::File::open(entry.path()).await?;