The try-catch clauses in MysqlInstaller.php attempt to use the method ->getText() from the class DBQueryError, but neither this class nor its parents do declare such method. Trying to run the installer fails with an error message from PHP:
PHP Fatal error: Call to undefined method Wikimedia\Rdbms\DBQueryError::getText() in /home/mwuser/mediawiki/includes/installer/MysqlInstaller.php on line 597
Edit: This also appears to be the case in MssqlInstaller.php
Steps to reproduce:
Try running install.php with the dbuser and dbpass flags set to a user that already exists, with installdbuser an installdbpass set as well.