Use the correct spanish translation

Translation has been updated so we need to use the correct spanish
word

spec/system/admin/unit_price_spec.rb

@@ -66,13 +66,14 @@
     it "creating a new variant with a comma separated decimal price" do
       product = create(:simple_product, variant_unit: "weight", variant_unit_scale: "1")
       login_as_admin
+
       visit spree.admin_dashboard_path(locale: 'es')
       visit spree.admin_product_variants_path product
       click_link 'Nueva Variante'
 
       tomselect_select "Peso (g)", from: "Unit scale"
-      click_on "Unit" # activate popout
-      fill_in "Unit value", with: "1"
+      click_on "Unidad" # activate popout
+      fill_in "Valor unidad", with: "1"
       fill_in 'Precio', with: '1,5'
 
       expect(find_field("Precio por unidad", disabled: true).value).to eq '1.500,00 $ / kg'