bind to localhost:0 for tests (#22839)

* bind to localhost:0 for tests

Explicitly bind to `localhost:0` instead of just `:0` to avoid binding to all available interfaces and in turn avoid triggering firewall warnings on MacOS.

* fix Playbooks to use dynamic port

* TestMetrics: handle ipv4 localhost too

* TestMetrics: linting

server/channels/web/web_test.go

@@ -107,7 +107,7 @@ func setupTestHelper(tb testing.TB, includeCacheLayer bool) *TestHelper {
 
 	a := app.New(app.ServerConnector(s.Channels()))
 	prevListenAddress := *s.Config().ServiceSettings.ListenAddress
-	a.UpdateConfig(func(cfg *model.Config) { *cfg.ServiceSettings.ListenAddress = ":0" })
+	a.UpdateConfig(func(cfg *model.Config) { *cfg.ServiceSettings.ListenAddress = "localhost:0" })
 	serverErr := s.Start()
 	if serverErr != nil {
 		panic(serverErr)