Add require to failing multi_db test

This started failing related to the removal of the classic autoloader.
This adds the require of environment.rb that other tests already had.

Author: jhawthorn

railties/test/application/rake/multi_dbs_test.rb

@@ -478,6 +478,7 @@ def generate_models_for_animals
       end
 
       test "db:schema:load:name sets the connection back to its original state" do
+        require "#{app_path}/config/environment"
         Dir.chdir(app_path) do
           dummy_task = <<~RUBY
             task foo: :environment do