Fix test with symfony/config:^7.2

[alexandre-daubois]

Following symfony/symfony#58490 (comment). Until the Symfony PR, null wasn't supported in boolean nodes and defaulted to true.

[derrabus]

Thank you. Your change makes our test suite green again, which is great of course. But, are we sure this subtle change in behavior won't break stuff downstream?

[alexandre-daubois]

I had a look while creating the PR, and it seems the null possibility was actually handled, even if not possible until now :

monolog-bundle/DependencyInjection/MonologExtension.php

Lines 180 to 182 in ed0e4a2

	if (null === $handler['process_psr_3_messages']['enabled']) {
	$handler['process_psr_3_messages']['enabled'] = !isset($handler['handler']) && !$handler['members'];
	}