[Cache] fix warning on PHP 7.4

Author: Julien Pauli

ParserCache/ParserCacheAdapter.php

@@ -30,7 +30,7 @@ public function __construct(ParserCacheInterface $pool)
         $this->pool = $pool;
 
         $this->createCacheItem = \Closure::bind(
-            function ($key, $value, $isHit) {
+            static function ($key, $value, $isHit) {
                 $item = new CacheItem();
                 $item->key = $key;
                 $item->value = $value;