fix: Update prompt retrieval method to use only prompts with type prompt

Author: butschster

src/McpServer/Action/Prompts/ListPromptsAction.php

@@ -34,7 +34,7 @@ public function __invoke(ServerRequestInterface $request): ListPromptsResult
             $prompts[] = $prompt;
         }
 
-        foreach ($this->prompts->all() as $prompt) {
+        foreach ($this->prompts->getItems() as $prompt) {
             $prompts[] = $prompt->prompt;
         }