MDL-77350 cache: Added class properties that are not declared

In PHP 8.2 and later, setting a value to an undeclared class property is
deprecated and emits a deprecation notice.
So we need to add missing class properties that still need to be declared.

cache/classes/config.php

@@ -65,6 +65,12 @@ class cache_config {
      */
     protected $configdefinitionmappings = array();
 
+    /**
+     * The locking mappings that have been configured.
+     * @var array
+     */
+    protected $configlockmappings = [];
+
     /**
      * An array of configured cache lock instances.
      * @var array