fix: encode request body as JSON in ActionCaller

Author: butschster

src/Routing/ActionCaller.php

@@ -32,7 +32,7 @@ public function __invoke(ServerRequestInterface $request): mixed
             $inputSchema = $inputSchemaClass->newInstance();
 
             $input = $this->schemaMapper->toObject(
-                json: (array)($request->getParsedBody() ?? []),
+                json: \json_encode((array)($request->getParsedBody() ?? [])),
                 class: $inputSchema->class,
             );