test_gossip_node: Use random port (#31490)

Using a fixed port could cause a false negative, if the port is
currently in use.  We actually see this test failing regularly with an
error that port `1111` is already in use.

Quick search did not show any tests that hardcode port 1111, so it is
unclear why is this happening.  But using hardcoded ports is not a good
practice anyways.

gossip/src/cluster_info.rs

@@ -3236,7 +3236,7 @@ mod tests {
         ));
         let (node, _, _) = ClusterInfo::gossip_node(
             solana_sdk::pubkey::new_rand(),
-            &"1.1.1.1:1111".parse().unwrap(),
+            &"1.1.1.1:0".parse().unwrap(),
             0,
         );
         assert!(ClusterInfo::is_spy_node(