Change code style badge

Change the XO code style badge to the [official version](https://github.com/xojs/xo?tab=readme-ov-file#badge). Before: <img width="155" alt="image" src="https://github.com/user-attachments/assets/e893810a-6d4e-47b1-ac78-f0fb79832fdb" /> After: <img width="158" alt="image" src="https://github.com/user-attachments/assets/5faa98fa-fcef-471e-9627-d1210469d770" />