fix(openapi): correct example usage

In OpenApi both `example` and `examples` keyword exist.
The difference relies in the fact that `example` takes one (or more) *anonymous example* whereas `examples` requires *named examples*.

Author: Fylax

src/State/ApiResource/Error.php

@@ -104,7 +104,7 @@ public function __construct(
             identifier: true,
             writable: false,
             initializable: false,
-            schema: ['type' => 'number', 'examples' => [404], 'default' => 400]
+            schema: ['type' => 'number', 'example' => [404], 'default' => 400]
         )] private int $status,
         ?array $originalTrace = null,
         private ?string $instance = null,