Fix template for existing Rails 7.1 applications

Rails 7.1 has changed the behaviour of applying a template to an existing application.
rails/rails@83e69c2
Because of this, we only need to explicitly run `after_bundle` actions
when applying the template to existing Rails applications prior to 7.1.

Fixes #1743

APP_TEMPLATE

@@ -82,5 +82,5 @@ after_bundle do
 end
 
 profile.for_existing_app do
-  run_after_bundle_callbacks
-end
+  run_after_bundle_callbacks if Gem::Version.new(Rails.version) < Gem::Version.new("7.1.0")
+end