Update astro monorepo

| datasource | package          | from  | to     |
| ---------- | ---------------- | ----- | ------ |
| npm        | @astrojs/mdx     | 3.1.7 | 3.1.9  |
| npm        | @astrojs/rss     | 4.0.7 | 4.0.12 |
| npm        | @astrojs/sitemap | 3.2.0 | 3.4.1  |

Author: renovate[bot]