Symfony version(s) affected: 5.1

Description

After upgrading to 5.1 my tests suddenly started failing on memory limit. So I ran them through blackfire and found out that between Symfony 5.0 and 5.1 the memory usage in my tests increased from < 500 MB to over 1.2 GB.

Then I tried to upgrade just a few packages at a time to find out which one was causing it and the culprit is symfony/doctrine-bridge. More specifically, the changes in Symfony\Bridge\Doctrine\Form\Type\DoctrineType class. When I revert just this class to it's 5.0 version, the problem disappears.

Git blame leads me to #30994 as the most likely cause.

cc @HeahDude