Make sure hidden users are shown in order

The test "Action links remember the pagination setting and the filter"
was failing sometimes because it assumed the third user created was
going to appear in the third place, but that wasn't always the case.

So we're using the same order we use in the rest of the sections dealing
with hidden content.

app/controllers/admin/hidden_users_controller.rb

@@ -4,7 +4,7 @@ class Admin::HiddenUsersController < Admin::BaseController
   before_action :load_user, only: [:confirm_hide, :restore]
 
   def index
-    @users = User.only_hidden.send(@current_filter).page(params[:page])
+    @users = User.only_hidden.send(@current_filter).order(hidden_at: :desc).page(params[:page])
   end
 
   def show

spec/system/admin/hidden_users_spec.rb

@@ -83,7 +83,7 @@ describe "Admin hidden users", :admin do
 
     visit admin_hidden_users_path(filter: "with_confirmed_hide", page: 2)
 
-    accept_confirm("Are you sure? Restore \"#{users[2].name}\"") do
+    accept_confirm("Are you sure? Restore \"#{users[-3].name}\"") do
       click_button "Restore", match: :first, exact: true
     end