Update test/parallel/test-net-server-simultaneous-accepts-produce-warning-once.js

Author: Trott

test/parallel/test-net-server-simultaneous-accepts-produce-warning-once.js

@@ -16,5 +16,8 @@ process.on(
   })
 );
 
+process.on('warning', mustCall(() => {
+  process.on('warning', mustNotCall());
+}));
 net._setSimultaneousAccepts();
 net._setSimultaneousAccepts();