/usr/share/php/Symfony/Bridge/Monolog/ is in php-symfony-monolog-bridge 2.7.10-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/php/Symfony/Bridge/Monolog/Formatter/
/usr/share/php/Symfony/Bridge/Monolog/Formatter/ConsoleFormatter.php
/usr/share/php/Symfony/Bridge/Monolog/Handler/
/usr/share/php/Symfony/Bridge/Monolog/Handler/ChromePhpHandler.php
/usr/share/php/Symfony/Bridge/Monolog/Handler/ConsoleHandler.php
/usr/share/php/Symfony/Bridge/Monolog/Handler/DebugHandler.php
/usr/share/php/Symfony/Bridge/Monolog/Handler/FingersCrossed/
/usr/share/php/Symfony/Bridge/Monolog/Handler/FingersCrossed/NotFoundActivationStrategy.php
/usr/share/php/Symfony/Bridge/Monolog/Handler/FirePHPHandler.php
/usr/share/php/Symfony/Bridge/Monolog/Handler/SwiftMailerHandler.php
/usr/share/php/Symfony/Bridge/Monolog/Logger.php
/usr/share/php/Symfony/Bridge/Monolog/Processor/
/usr/share/php/Symfony/Bridge/Monolog/Processor/WebProcessor.php
/usr/share/php/Symfony/Bridge/Monolog/autoload.php