chore: fix type cast when using declare(strict_types=1);

Author: Crovitche-1623

src/Persistence/Repository/ResetPasswordRequestRepositoryTrait.php

@@ -22,7 +22,7 @@ trait ResetPasswordRequestRepositoryTrait
 {
     public function getUserIdentifier(object $user): string
     {
-        return $this->getEntityManager()
+        return (string) $this->getEntityManager()
             ->getUnitOfWork()
             ->getSingleIdentifierValue($user)
         ;