Symfony version(s) affected: Upgrade from 4.3 to 4.4

Description
Symfony does not log any deprecation in my log.

How to reproduce
Minimal Example (created with 4.3 skeleton and upgraded to 4.4):

git clone https://github.com/oceanBT/symfony-deprecation-log
cd symfony-deprecation-log
composer install
bin/console server:run

curl http://localhost:8000/test

tail -f var/log/*.log  # no deprecations got logged :/

Changed files:
https://github.com/oceanBT/symfony-deprecation-log/blob/master/config/packages/dev/monolog.yaml (but also original config does not work)

https://github.com/oceanBT/symfony-deprecation-log/blob/master/src/Controller/TestController.php#L26

.env:
APP_ENV=dev