Flag test_tvu_exit as serial to hopefully reduce CI flakiness (#9509)

core/src/tvu.rs

@@ -266,12 +266,14 @@ pub mod tests {
     use super::*;
     use crate::banking_stage::create_test_recorder;
     use crate::cluster_info::{ClusterInfo, Node};
+    use serial_test_derive::serial;
     use solana_ledger::create_new_tmp_ledger;
     use solana_ledger::genesis_utils::{create_genesis_config, GenesisConfigInfo};
     use solana_runtime::bank::Bank;
     use std::sync::atomic::Ordering;
 
     #[test]
+    #[serial]
     fn test_tvu_exit() {
         solana_logger::setup();
         let leader = Node::new_localhost();