This is blocking a PullRequest in the moodle-plugin-ci repository. The error displayed is:

PHP Deprecated:  behat_app::i_enter_the_app(): Implicitly marking parameter  
   $username as nullable is deprecated, the explicit nullable type must be us  
  ed instead in /home/runner/work/moodle-plugin-ci/moodle-plugin-ci/moodle/lo  
  cal/moodleappbehat/tests/behat/behat_app.php on line 104