Update typed property array => ArrayCollection to prevent errors

When using strict type checking you could get errors like:
```
TypeError: Cannot assign Doctrine\Common\Collections\ArrayCollection to property App\Entity\Category::$products of type array
```

Co-authored-by: Christian Flothmann <christian.flothmann@gmail.com>

Author: JohJohan

doctrine/associations.rst

@@ -220,7 +220,7 @@ class that will hold these objects:
             // ...
 
             #[ORM\OneToMany(targetEntity: Product::class, mappedBy: 'category')]
-            private array $products;
+            private Collection $products;
 
             public function __construct()
             {