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/pgp.rs

@@ -17,7 +17,7 @@ use pgp::crypto::hash::HashAlgorithm;
 use pgp::crypto::sym::SymmetricKeyAlgorithm;
 use pgp::packet::{SignatureConfig, SignatureType, Subpacket, SubpacketData};
 use pgp::types::{CompressionAlgorithm, KeyDetails, Password, PublicKeyTrait, StringToKey};
-use rand::thread_rng;
+use rand_old::thread_rng;
 use tokio::runtime::Handle;
 
 use crate::key::{DcKey, Fingerprint};