test: add test for _setSimultaneousAccepts()

Add a test case that verifies that calling _setSimultaneousAccepts()
function twice does not trigger the deprecation warning twice.

PR-URL: https://github.com/nodejs/node/pull/24180
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

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

@@ -0,0 +1,12 @@
+'use strict';
+
+const { expectWarning } = require('../common');
+const net = require('net');
+
+expectWarning(
+  'DeprecationWarning',
+  'net._setSimultaneousAccepts() is deprecated and will be removed.',
+  'DEP0121');
+
+net._setSimultaneousAccepts();
+net._setSimultaneousAccepts();