Change unit_type warning to a hard error

app/models/product_import/entry_validator.rb

@@ -13,7 +13,6 @@ def initialize(current_user, import_time, spreadsheet_data, editable_enterprises
     def non_updatable_fields
       {
         category: :primary_taxon_id,
-        unit_type: :variant_unit_scale,
         variant_unit_name: :variant_unit_name,
         tax_category: :tax_category_id,
         shipping_category: :shipping_category_id
@@ -178,6 +177,11 @@ def product_validation(entry)
         return
       end
 
+      if existing_product.variant_unit_scale != entry.variant_unit_scale
+        mark_as_invalid(entry, attribute: "unit_type", error: I18n.t('admin.product_import.model.not_updatable'))
+        return
+      end
+
       # Otherwise, if a variant exists with matching display_name and unit_value, update it
       existing_product.variants.each do |existing_variant|
         if entry_matches_existing_variant?(entry, existing_variant) && existing_variant.deleted_at.nil?

config/locales/en.yml

@@ -489,7 +489,7 @@ en:
         conditional_blank: can't be blank if unit_type is blank
         no_product: did not match any products in the database
         not_found: not found in database
-        not_updatable: cannot be updated on existing products
+        not_updatable: cannot be updated on existing products via product import
         blank: can't be blank
         products_no_permission: you do not have permission to manage products for this enterprise
         inventory_no_permission: you do not have permission to create inventory for this producer