minor #17821 [Doctrine] Update example to match actual make::entity output (alamirault)

This PR was merged into the 5.4 branch.

Discussion
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[Doctrine] Update example to match actual make::entity output

From slack

![image](https://user-images.githubusercontent.com/9253091/215199944-ecc4544f-62c8-435d-928d-e219b1c5e732.png)

It's a new behavior since maker 1.44.0 released July 26th, 2022
symfony/maker-bundle#1147

(New example is based on local execution)

Commits
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32d50e9 Update example to match actual make::entity output

Author: javiereguiluz

doctrine.rst

@@ -135,19 +135,19 @@ Whoa! You now have a new ``src/Entity/Product.php`` file::
     use App\Repository\ProductRepository;
     use Doctrine\ORM\Mapping as ORM;
 
-     #[ORM\Entity(repositoryClass: ProductRepository::class)]
+    #[ORM\Entity(repositoryClass: ProductRepository::class)]
     class Product
     {
         #[ORM\Id]
         #[ORM\GeneratedValue]
         #[ORM\Column]
-        private int $id;
+        private ?int $id = null;
 
         #[ORM\Column(length: 255)]
-        private string $name;
+        private ?string $name = null;
 
         #[ORM\Column]
-        private int $price;
+        private ?int $price = null;
 
         public function getId(): ?int
         {