Explicitly load required file

This will be required if fixing FactoryBot/FactoryClassName
I'm not 100% sure about that rule yet, but figured this fix was worth keeping.

spec/lib/spree/localized_number_spec.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require 'spec_helper'
+require 'spree/localized_number'
 
 describe Spree::LocalizedNumber do
   describe ".parse" do