#Needs reroll

So in fact the claro_help_search block was missing a UUID and this in turn triggered an error via \Drupal\Core\Config\Entity\ConfigEntityBase::preSave() when checking for existing entities with that UUID over in \Drupal\Core\Config\Entity\Query\Condition::compile() because that results in mb_strtolower() being called with NULL. Fun!

Let's see if this is better. The test passes now with a deprecation, but I think that's correct as update tests inherently trigger deprecations before the update... but we'll see.

Hit this as well. As an extra cherry on top, what happened for me is - because the value is currently incorrectly maked as translatable - that on a multilingual all my block labels are suddenly "sichtbar" (which means visible in German).

Rebased and squashed. I "manually" diffed the change in core/modules/system/tests/fixtures/update/drupal-10.3.0.filled.standard.php.gz but could not find a meaningful difference, so just ended up reverting that, let's see if this passes or not.