Explicitly require symfony/property-access

Since symfony/symfony#43534 (released with `symfony/serializer` 6.2.0),
Symfony's ObjectNormalizer has a hard dependency to the
`symfony/property-access` package. As we're using the ObjectNormalizer,
we must ensure to meet this requirement by explicitly adding the
package as requirement in `composer.json`.

composer.json

@@ -28,6 +28,7 @@
         "symfony/config": "^4.4 || ^5.4 || ^6.0",
         "symfony/console": "^4.4 || ^5.4 || ^6.0",
         "symfony/dependency-injection": "^4.4.8 || ^5.4 || ^6.0",
+        "symfony/property-access": "^4.4 || ^5.4 || ^6.0",
         "symfony/serializer": "^4.4 || ^5.4 || ^6.0",
         "webmozart/assert": "^1.10",
         "webmozart/glob": "^4.4"