iTop limit pages/exec.php script to PHP files

iTop is an IT service management platform. Files from the `env-production` folder can be retrieved even though they should have restricted access. Hopefully, there is no sensitive files stored in that folder natively, but there could be from a third-party module. The `pages/exec.php` script as been fixed to limit execution of PHP files only. Other file types won't be retrieved and exposed. The vulnerability is fixed in 2.7.10, 3.0.4, 3.1.1, and 3.2.0.