Use form_tag in search form

This form does not depend on an object at all, so we can use a generic
tag which is model-independent.

app/components/admin/search_component.html.erb

@@ -1,9 +1,9 @@
 <div class="small-12 medium-6">
-  <%= form_for(User.new, url: url, as: :user, method: :get) do |f| %>
+  <%= form_tag(url, method: :get) do |f| %>
     <div class="input-group">
         <%= text_field_tag :name_or_email, params[:name_or_email].to_s, placeholder: t("admin.shared.user_search.placeholder") %>
       <div class="input-group-button">
-        <%= f.submit t("admin.shared.user_search.button"), class: "button" %>
+        <%= submit_tag t("admin.shared.user_search.button"), class: "button" %>
       </div>
     </div>
   <% end %>