Require action_dispatch fully

It uses autoload, so it's lazy-loaded. However there are missing some
internal requires so it will asks for more not-related `requires`
when requiring some files directly.

spec/telegram/bot/rspec/integration_spec.rb

@@ -1,7 +1,6 @@
 require 'telegram/bot/rspec/integration'
 require 'action_controller'
 require 'action_dispatch'
-require 'action_dispatch/testing/integration'
 
 RSpec.describe 'Integrations helper', :telegram_bot do
   include ActionDispatch::Integration::Runner