Issue #3283351 by Sweetchuck: PHP 8.1 Return type of...

Issue #3283351 by Sweetchuck: PHP 8.1 Return type of DeprecatedArray::unserialize() and ::serialize()

(cherry picked from commit df6d9bda)

core/lib/Drupal/Component/Utility/DeprecatedArray.php

@@ -75,6 +75,7 @@ public function getIterator() {
   /**
    * {@inheritdoc}
    */
+  #[\ReturnTypeWillChange]
   public function unserialize($serialized) {
     @trigger_error($this->message, E_USER_DEPRECATED);
     parent::unserialize($serialized);
@@ -83,6 +84,7 @@ public function unserialize($serialized) {
   /**
    * {@inheritdoc}
    */
+  #[\ReturnTypeWillChange]
   public function serialize() {
     @trigger_error($this->message, E_USER_DEPRECATED);
     return parent::serialize();