Fix LIMIT_UNLIMITED type issue (#140)

* Fix LIMIT_UNLIMITED type issue

* Update PHPDoc

* update phpdoc comment

---------

Co-authored-by: Florian Tinney <florian.tinney@elbkapitaene.de>
Co-authored-by: JiaJia Ji <kingjia90@gmail.com>

src/IndexService/ProductList/ElasticSearch/AbstractElasticSearch.php

@@ -28,7 +28,7 @@
 
 abstract class AbstractElasticSearch implements ProductListInterface
 {
-    const LIMIT_UNLIMITED = 'unlimited';
+    const LIMIT_UNLIMITED = -1;
 
     const INTEGER_MAX_VALUE = 2147483647;     // Elasticsearch Integer.MAX_VALUE is 2^31-1
 
@@ -321,19 +321,19 @@ public function getOrderKey(): array|string
     }
 
     /**
-     * Pass "unlimited" to do da Scroll Request
+     * Pass -1 to enable the unlimited scroll request
      *
      * @param int $limit
      *
      * @return void
      */
     public function setLimit(int $limit): void
     {
-        if ($this->limit != $limit) {
+        if ($this->limit !== $limit) {
             $this->products = null;
         }
 
-        if ($limit == static::LIMIT_UNLIMITED) {
+        if ($limit === static::LIMIT_UNLIMITED) {
             $this->limit = 100;
             $this->doScrollRequest = true;
         } else {