Avoid global state change by using config stub

spec/support/localized_number_helper.rb

@@ -1,10 +1,6 @@
 shared_examples "a model using the LocalizedNumber module" do |attributes|
   before do
-    Spree::Config[:enable_localized_number?] = true
-  end
-
-  after do
-    Spree::Config[:enable_localized_number?] = false
+    allow(Spree::Config).to receive(:enable_localized_number?).and_return true
   end
 
   attributes.each do |attribute|