test: use random port in NodeInstance.startViaSignal()

Which makes it possible to run the tests that use this in parallel.

PR-URL: nodejs#47412
Refs: nodejs#47146
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/common/inspector-helper.js

@@ -372,7 +372,7 @@ class NodeInstance extends EventEmitter {
 
   static async startViaSignal(scriptContents) {
     const instance = new NodeInstance(
-      ['--expose-internals'],
+      ['--expose-internals', '--inspect-port=0'],
       `${scriptContents}\nprocess._rawDebug('started');`, undefined);
     const msg = 'Timed out waiting for process to start';
     while (await fires(instance.nextStderrString(), msg, TIMEOUT) !== 'started');