FIX: Failed to restore backups from versions without translation overrides

Rails calls I18n.translate during initialization and by default translation overrides are used. Database migrations would fail if the system tried to migrate from an old version that didn't have the `translation_overrides` table with all its columns yet.

This makes restoring really old backups work again. Running `DISABLE_TRANSLATION_OVERRIDES=1 rake db:migrate` will allow you to upgrade such an old database as well.

spec/lib/backup_restore/database_restorer_spec.rb

@@ -38,6 +38,7 @@ describe BackupRestore::DatabaseRestorer do
     Discourse::Utils.expects(:execute_command).with do |env, command, options|
       env["SKIP_POST_DEPLOYMENT_MIGRATIONS"] == "0" &&
         env["SKIP_OPTIMIZE_ICONS"] == "1" &&
+        env["DISABLE_TRANSLATION_OVERRIDES"] == "1" &&
         command == "rake db:migrate" &&
         options[:chdir] == Rails.root
     end.once