minor #18727 Update typed property array => ArrayCollection to prevent errors (johanadivare)

This PR was merged into the 6.3 branch.

Discussion
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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
```

Commits
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01d76d3 Update typed property array => ArrayCollection to prevent errors

Author: javiereguiluz

Diff for: 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()
             {