Use headless Chrome for system tests

1) Avoids opening a Chrome window locally
2) Allows system tests to run on GitHub Actions

Author: vangberg

test/application_system_test_case.rb

@@ -1,5 +1,5 @@
 require 'test_helper'
 
 class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
-  driven_by :selenium, using: :chrome, screen_size: [1400, 1400]
+  driven_by :selenium, using: :headless_chrome, screen_size: [1400, 1400]
 end