docs: fix custom filter usage on several properties (#2066)

core/filters.md

@@ -1651,7 +1651,7 @@ use ApiPlatform\Core\Annotation\ApiResource;
 use App\Filter\CustomAndFilter;
 
 #[ApiResource]
-#[ApiFilter(CustomAndFilter::class, properties={"name", "cost"})]
+#[ApiFilter(CustomAndFilter::class, properties=["name", "cost"])]
 class Offer
 {
     // ...