fix: rendre le champ "E-mail de secours" nullable dans l'entité User

src/Entity/User.php

@@ -191,7 +191,7 @@ class User implements UserInterface, PasswordAuthenticatedUserInterface
         return $this->alternateEmail;
     }
 
-    public function setAlternateEmail(string $alternateEmail): static
+    public function setAlternateEmail(?string $alternateEmail): static
     {
         $this->alternateEmail = $alternateEmail;