Add temporary fix to enable headless invitation lists tests

[gazayas]

Fixes #1029.

For some reason in the Invitation List tests only, we get the following value.

     5: def setup
 =>  6:   binding.pry
     7: 
     8:   @current_bulk_invitations_setting = nil
     9:   BulletTrain.configure do |config|
    10:     @current_bulk_invitations_setting = config.enable_bulk_invitations
    11:     config.enable_bulk_invitations = true
    12:   end
    13: end

[1] pry(#<InvitationListsTest>)> Capybara.current_driver
=> :selenium

However, in application_system_test_case.rb, we only set one of these two keys explicitly.

bullet_train/test/application_system_test_case.rb

Lines 26 to 27 in d95deaa

	Capybara.javascript_driver = ENV["MAGIC_TEST"].present? ? :selenium_chrome : :selenium_chrome_headless
	Capybara.default_driver = ENV["MAGIC_TEST"].present? ? :selenium_chrome : :selenium_chrome_headless

I'm guessing this is related to #1028 especially since it's a Selenium::Webdriver error that's being raised, but I'll have to investigate further to make sure.

[gazayas]

Passing consistently now

[jagthedrummer]

Wow, good find! I don't think it would have even occurred to me to check that.