Downsize tcp-stress.rs again

Author: jieyouxu

tests/ui/threads-sendsync/tcp-stress.rs

@@ -11,7 +11,10 @@ use std::sync::mpsc::channel;
 use std::thread::{self, Builder};
 use std::time::Duration;
 
-const TARGET_CNT: usize = 200;
+// NOTE(#144878): even though this is technically a stress test, only limit to 100 threads, because
+// sometimes the runner might be busy and can't cleanup the previous count of 200 threads in time,
+// triggering timeout flaky failures.
+const TARGET_CNT: usize = 100;
 
 fn main() {
     // This test has a chance to time out, try to not let it time out