<div class="promotion_action promotion-block <%= promotion_action.type.to_s.demodulize.underscore %>" id="<%= dom_id promotion_action %>">
  <% type_name = promotion_action.class.name.demodulize.underscore %>
  <h6 class="promotion-title"><%= promotion_action.class.human_attribute_name(:description) %></h6>
  <% if can?(:destroy, promotion_action) %>
    <%= link_to_with_icon 'trash', '', spree.admin_promotion_promotion_action_path(@promotion, promotion_action), remote: true, method: :delete, class: 'delete' %>
  <% end %>

  <% param_prefix = "promotion[promotion_actions_attributes][#{promotion_action.id}]" %>
  <%= hidden_field_tag "#{param_prefix}[id]", promotion_action.id %>

  <%= render partial: "spree/shared/error_messages", locals: { target: promotion_action } %>
  <%= render partial: "spree/admin/promotions/actions/#{type_name}",
             locals: { promotion_action: promotion_action, param_prefix: param_prefix } %>
</div>

<div class="promotion_action promotion-block <%= promotion_action.model_name.element %>" id="<%= dom_id promotion_action %>">
  <% type_name = promotion_action.model_name.element %>
  <h6 class="promotion-title"><%= promotion_action.class.human_attribute_name(:description) %></h6>
  <% if can?(:destroy, promotion_action) %>
    <%= link_to_with_icon 'trash', '', spree.admin_promotion_promotion_action_path(@promotion, promotion_action), remote: true, method: :delete, class: 'delete' %>
  <% end %>

  <% param_prefix = "promotion[promotion_actions_attributes][#{promotion_action.id}]" %>
  <%= hidden_field_tag "#{param_prefix}[id]", promotion_action.id %>

  <%= render partial: "spree/shared/error_messages", locals: { target: promotion_action } %>
  <%= render partial: "spree/admin/promotions/actions/#{type_name}",
             locals: { promotion_action: promotion_action, param_prefix: param_prefix } %>
</div>

Use i18n model_name method for promo actions
Use i18n model_name method for promo actions

Instead of demodulizing we can use the provided i18n method to grab the
element name
