Scope the config option

Also use a `configure` block to set it up.

config/environments/test.rb

@@ -69,5 +69,5 @@ Rails.application.configure do
   config.autoload_paths += %w[ test/test_helpers ]
 
   # Enable multi-tenant mode for tests
-  config.x.multi_tenant = true
+  config.x.multi_tenant.enabled = true
 end

config/initializers/multi_tenant.rb

@@ -1,3 +1,5 @@
-Rails.application.config.after_initialize do
-  Account.multi_tenant = ENV["MULTI_TENANT"] == "true" || Rails.configuration.x.multi_tenant == true
+Rails.application.configure do
+  config.after_initialize do
+    Account.multi_tenant = ENV["MULTI_TENANT"] == "true" || config.x.multi_tenant.enabled == true
+  end
 end