minor #18519 [Form] Update entity.rst (rodmar35)

This PR was merged into the 6.3 branch.

Discussion
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[Form] Update entity.rst

Add "use Doctrine\ORM\QueryBuilder " dependencies else we have an error : "Return value must be of type App\Form\QueryBuilder, Doctrine\ORM\QueryBuilder returned"

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Commits
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4dcc7b8 Update entity.rst

Author: javiereguiluz

reference/forms/types/entity.rst

@@ -53,6 +53,7 @@ the `query_builder`_ option::
 
     use App\Entity\User;
     use Doctrine\ORM\EntityRepository;
+    use Doctrine\ORM\QueryBuilder;
     use Symfony\Bridge\Doctrine\Form\Type\EntityType;
     // ...