Align return type of getEntityFileUrl() with getFileUri().

src/Plugin/Field/FieldFormatter/TinySliderFieldFormatter.php

@@ -761,10 +761,10 @@ class TinySliderFieldFormatter extends EntityReferenceFormatterBase implements C
    * @param \Drupal\Core\Entity\EntityInterface $entity
    *   The entity.
    *
-   * @return \Drupal\Core\Url|null
-   *   The file URL if available.
+   * @return string|null
+   *   The file URI if available.
    */
-  protected function getEntityFileUrl(EntityInterface $entity): ?Url {
+  protected function getEntityFileUrl(EntityInterface $entity): ?string {
     if ($entity->getEntityTypeId() === 'file') {
       return $entity->getFileUri();
     }