minor #19572 Update serializer.rst (hbgamra)

This PR was submitted for the 7.0 branch but it was merged into the 5.4 branch instead.

Discussion
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Update serializer.rst

use php8 functions to manipulate string

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Commits
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711d27c Update serializer.rst

Author: OskarStark

components/serializer.rst

@@ -606,7 +606,7 @@ A custom name converter can handle such cases::
         public function denormalize(string $propertyName)
         {
             // removes 'org_' prefix
-            return 'org_' === substr($propertyName, 0, 4) ? substr($propertyName, 4) : $propertyName;
+            return str_starts_with($propertyName, 'org_') ? substr($propertyName, 4) : $propertyName;
         }
     }