Drupal 10 minimum PHP requirement raised to PHP 8.0.0

Drupal 10's minimum PHP version requirements was raised to PHP 8.0.0. It will not be possible to run Drupal 10 on PHP 7 or earlier. However, there is a possibility that before Drupal 10's release, the PHP requirement will be raised again to PHP 8.1. See #3173787: [policy] Require PHP 8.1 for Drupal 10.0 if a dependency does, otherwise require PHP 8.0. (up from 7.3 in Drupal 9) for ongoing discussion.