test: use random port in test-inspector-debug-brk-flag

Which makes it possible to run it in parallel.

PR-URL: #47412
Refs: #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/sequential/test-inspector-debug-brk-flag.js

@@ -27,7 +27,7 @@ async function testBreakpointOnStart(session) {
 }
 
 async function runTests() {
-  const child = new NodeInstance(['--inspect', '--inspect-brk']);
+  const child = new NodeInstance(['--inspect-brk=0']);
   const session = await child.connectInspectorSession();
 
   await testBreakpointOnStart(session);