Fix flaky --exit integration timeout by avoiding a hard-coded port

[Copilot]

The --exit integration spec was intermittently failing because the test fixture bound a fixed local port. Under CI and busy environments, that can collide with other listeners or stale processes and make the “should hang when --no-exit is used” case fail even though the root suite behavior is correct.

• Changed the exit fixture to bind to an ephemeral port instead of a fixed port:
  • server.listen(0, done);
• This preserves the intended regression coverage: the test still verifies that Mocha does not force exit after the root suite completes when --no-exit behavior is in effect, without depending on a port that may already be in use.

it('should hang when --no-exit used', function (done) {
  var server = net.createServer();
  server.listen(0, done);
});

This keeps the test focused on the actual behavior under test and removes the flaky dependency on local port availability.

• Fixes 🛠️ Repo: flaky test: "--exit ... should not force exit after root suite completion" #6362

[linux-foundation-easycla]

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