Just removing the $logger property on the class is sufficient. That property ...

Just removing the $logger property on the class is sufficient. That property is made available by LoggerAwareTrait anyway and the error was due to different types (it needed to be `?LoggerInterface` whereas it was missing and assumed `mixed` in the module's class).

We can still set to the property in the constructor because LoggerInterface is compatible with Drupal's `\Drupal\Core\Logger\LoggerChannelInterface`.