Use a single string instead of array of strings

[MAILPOET-3625]

lib/Newsletter/Sending/ScheduledTasksRepository.php

@@ -46,19 +46,15 @@ class ScheduledTasksRepository extends Repository {
       ->getResult();
   }
 
-  /**
-   * @param string[] $types
-   * @return ScheduledTaskEntity|null
-   */
-  public function findScheduledOrRunningTask(array $types = []): ?ScheduledTaskEntity {
+  public function findScheduledOrRunningTask(?string $type): ?ScheduledTaskEntity {
     $queryBuilder = $this->doctrineRepository->createQueryBuilder('st')
       ->select('st')
       ->where('(st.status = :scheduledStatus) OR (st.status is NULL)')
       ->setParameter('scheduledStatus', ScheduledTaskEntity::STATUS_SCHEDULED);
-    if (!empty($types)) {
+    if (!empty($type)) {
       $queryBuilder
-        ->andWhere('st.type in (:types)')
-        ->setParameter('types', $types);
+        ->andWhere('st.type = :type')
+        ->setParameter('type', $type);
     }
     return $queryBuilder->getQuery()->getOneOrNullResult();
   }