Add missing comma to routes error message

Co-authored-by: Hannah Content <hannah.cooper@digital.cabinet-office.gov.uk>

Author: thomasiles

config/locales/en.yml

@@ -367,7 +367,7 @@ en:
     prefix: 'Error:'
     routes:
       cannot_route_backwards_from_generic_page: The route from question %{question_number} cannot go to a previous question - edit this route
-      cannot_route_backwards_from_selection_page: The route from question %{question_number}, option %{option_number}, cannot go to a previous question - edit this route
+      cannot_route_backwards_from_selection_page: The route from question %{question_number}, option %{option_number} cannot go to a previous question - edit this route
       page_list:
         cannot_route_backwards_from_generic_page: The route from question %{question_number} cannot go to a previous question - edit this route
         cannot_route_backwards_from_selection_page: