[BUGFIX] Fix undefined array key with PHP 8 in FinisherRunner

Resolves: #778

Author: einpraegsam

Classes/Finisher/FinisherRunner.php

@@ -52,7 +52,7 @@ public function callFinishers(
                 $finisher = GeneralUtility::makeInstance(
                     $class,
                     $mail,
-                    (array)$finisherSettings['config'] ?? [],
+                    $finisherSettings['config'] ?? [],
                     $settings,
                     $formSubmitted,
                     $actionMethodName,