When running maintenance/changePassword.php on a local instance (on a Windows server) I get the following warnings.
It's unclear if the password change went through (since the password was reset to what it should have been initially)
PHP Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in C:\inetpub\wwwroot\mediawiki\includes\session\PHPSessionHandler.php on line 126 PHP Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in C:\inetpub\wwwroot\mediawiki\includes\session\PHPSessionHandler.php on line 127 PHP Warning: session_cache_limiter(): Cannot change cache limiter when headers already sent in C:\inetpub\wwwroot\mediawiki\includes\session\PHPSessionHandler.php on line 133 PHP Warning: session_set_save_handler(): Cannot change save handler when headers already sent in C:\inetpub\wwwroot\mediawiki\includes\session\PHPSessionHandler.php on line 140