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/key.rs

@@ -11,7 +11,6 @@ use pgp::composed::Deserializable;
 pub use pgp::composed::{SignedPublicKey, SignedSecretKey};
 use pgp::ser::Serialize;
 use pgp::types::{KeyDetails, KeyId, Password};
-use rand::thread_rng;
 use tokio::runtime::Handle;
 
 use crate::context::Context;
@@ -314,7 +313,7 @@ impl DcSecretKey for SignedSecretKey {
     fn split_public_key(&self) -> Result<SignedPublicKey> {
         self.verify()?;
         let unsigned_pubkey = self.public_key();
-        let mut rng = thread_rng();
+        let mut rng = rand_old::thread_rng();
         let signed_pubkey = unsigned_pubkey.sign(
             &mut rng,
             &self.primary_key,