Added missing array return declaration

Author: jekuaitk

modules/os2forms_digital_post/src/EventSubscriber/Os2formsDigitalPostSubscriber.php

@@ -113,6 +113,8 @@ public function setDigitalPostContext(WebformSubmissionInterface $submission, Co
 
   /**
    * Check for Digital Post context in the current session.
+   *
+   * @return array<string, mixed>|null
    */
   public function getDigitalPostContext(WebformSubmissionInterface $submission): ?array {
     $key = $this->createSessionKeyFromSubmission($submission);