Add fieldset title to shipping methods edit form

app/views/spree/admin/shipping_methods/_form.html.haml

@@ -47,6 +47,7 @@
   = render partial: 'spree/admin/shared/calculator_fields', locals: { f: f }
 
   %fieldset.tax_categories.no-border-bottom
+    %legend{align: "center"}= t('.tax_category')
     = f.field_container :tax_categories do
       = f.select :tax_category_id, @tax_categories.map { |tc| [tc.name, tc.id] }, {}, :class => "select2 fullwidth"
       = error_message_on :shipping_method, :tax_category_id

config/locales/en.yml

@@ -3525,6 +3525,7 @@ See the %{link} to find out more about %{sitename}'s features and to start using
           back_to_shipping_methods_list: "Back To Shipping Methods List"
         form:
           categories: "Categories"
+          tax_category: "Tax Category"
           zones: "Zones"
           both: "Both Checkout and Back office"
           back_end: "Back office only"