FIX: Make form use /u/admin-login instead of /users/admin-login (#10663)

app/views/users/admin_login.html.erb

@@ -2,9 +2,9 @@
   <%= @message %>
   <% if @error %><p><%= @error %></p><% end %>
 <% else %>
-  <%=form_tag({}, method: :put) do %>
+  <%=form_tag(u_admin_login_path, method: :put) do %>
     <%= label_tag(:email, t('admin_login.email_input')) %>
     <%= text_field_tag(:email, nil, autofocus: true) %><br><br>
     <%= submit_tag t('admin_login.submit_button'), class: "btn btn-primary" %>
   <% end %>
-<% end %>
+<% end %>