Fix PHP 8.2 compatibility issue

Closes #3358292

tests/src/Kernel/SchemaFactoryTest.php

@@ -36,6 +36,13 @@ class SchemaFactoryTest extends KernelTestBase {
     'user',
   ];
 
+  /**
+   * node type.
+   *
+   * @var \Drupal\node\Entity\NodeType
+   */
+  protected $nodeType;
+
   /**
    * {@inheritdoc}
    */