[ticket/10840] Add check_form_key to acp_groups.php

PHPBB3-10840
Merge remote-tracking branch 'nickvergessen/ticket/10840' into develop-olympus

* nickvergessen/ticket/10840:
  [ticket/10840] Add check_form_key to acp_groups.php
Merge branch 'develop-olympus' into develop

* develop-olympus:
  [ticket/10840] Add check_form_key to acp_groups.php