Update Product Link form for Alchemy 7.1

Alchemy 7.1 now allows to submit the form like
any other form with Enter key and prevents submits
correctly.

This still works with Alchemy 6.1 and 7.0 because of
the data attribute we kept on the button tag.

app/views/alchemy/admin/pages/_product_link.html.erb

@@ -1,4 +1,4 @@
-<%= form_tag do %>
+<form data-link-form-type="product">
   <%= render_message do %>
     <h3><%= Alchemy.t(:choose_product_to_link) %></h3>
   <% end %>
@@ -23,8 +23,8 @@
       class: 'alchemy_selectbox link_target' %>
   </div>
   <div class="submit">
-    <%= button_tag Alchemy.t(:apply), class: 'create-link button', data: { link_type: 'product' } %>
+    <%= button_tag Alchemy.t(:apply), class: "create-link", data: { link_type: "product" } %>
   </div>
-<% end %>
+</form>
 
 <%= render "product_link_script" %>