Fix \Drupal\migrate\Plugin\migrate\destination\EntityConfigBase::updateEntity() to not trigger deprecations in PHP 8.1

Problem/Motivation

The following code causes a deprecation in PHP 8.1.

$config_override->set(str_replace(Row::PROPERTY_SEPARATOR, '.', $row->getDestinationProperty('property')), $row->getDestinationProperty('translation'));

It's because $row->getDestinationProperty('property') returns NULL. So one fix would be to do (string) $row->getDestinationProperty('property') - which is what happens in HEAD on other versions of PHP. However calling $config_override->set('', 'some value') does not make any sense so this needs more investigation.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet