minor symfony#58360 [Serializer] Fix test expectation (alexandre-daubois)

This PR was merged into the 7.2 branch.

Discussion
----------

[Serializer] Fix test expectation

| Q             | A
| ------------- | ---
| Branch?       | 7.2
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

Stumbled across the following error while running tests on recent PHPUnit version:

```
Only 12 return values have been configured for Symfony\Component\PropertyInfo\PropertyAccessExtractorInterface::isWritable()
```

Commits
-------

3ee2489 [Serializer] Fix expectation

Author: xabbuh

src/Symfony/Component/Validator/Tests/Mapping/Loader/PropertyInfoLoaderTest.php

@@ -126,6 +126,7 @@ public function getTypes(string $class, string $property, array $context = []):
                 true,
                 true,
                 false,
+                true,
                 true
             )
         ;