refactor(s2n-quic-dc): disable restart test on MacOS (#2839)

Author: boquan-fang

dc/s2n-quic-dc/src/stream/tests/restart.rs

@@ -199,6 +199,7 @@ mod tcp {
     tests!();
 }
 
+#[cfg(not(target_os = "macos"))]
 mod udp {
     use super::*;