Test: Re-create fix from Solidus PR 5991

Author: mamhoff

lib/solidus_dev_support/templates/extension/bin/sandbox.tt

@@ -30,7 +30,8 @@ echo "~~~> Removing the old sandbox"
 rm -rf ./sandbox
 
 echo "~~~> Creating a pristine Rails app"
-rails new sandbox \
+rails_version=`bundle exec ruby -e'require "rails"; puts Rails.version'`
+rails _${rails_version}_ new sandbox \
   --database="${DB:-sqlite3}" \
   --skip-git \
   --skip-keeps \