bug #50788 [Validator] Fix regression with class metadatada on parent classes (rmikalkenas)

This PR was merged into the 5.4 branch.

Discussion
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[Validator] Fix regression with class metadatada on parent classes

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix #50780
| License       | MIT

Commits
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e98f5f2782 [Validator] Fix regression with class metadatada on parent classes

Author: nicolas-grekas

Validator/DoctrineLoader.php

@@ -108,7 +108,7 @@ public function loadClassMetadata(ClassMetadata $metadata): bool
                 if (isset($mapping['originalClass']) && !str_contains($mapping['declaredField'], '.')) {
                     $metadata->addPropertyConstraint($mapping['declaredField'], new Valid());
                     $loaded = true;
-                } elseif (property_exists($className, $mapping['fieldName'])) {
+                } elseif (property_exists($className, $mapping['fieldName']) && (!$doctrineMetadata->isMappedSuperclass || $metadata->getReflectionClass()->getProperty($mapping['fieldName'])->isPrivate())) {
                     $metadata->addPropertyConstraint($mapping['fieldName'], new Length(['max' => $mapping['length']]));
                     $loaded = true;
                 }