Bump astro from 5.13.5 to 5.15.9

Bumps [astro](https://github.com/withastro/astro/tree/HEAD/packages/astro) from 5.13.5 to 5.15.9.
- [Release notes](https://github.com/withastro/astro/releases)
- [Changelog](https://github.com/withastro/astro/blob/main/packages/astro/CHANGELOG.md)
- [Commits](https://github.com/withastro/astro/commits/astro@5.15.9/packages/astro)

---
updated-dependencies:
- dependency-name: astro
  dependency-version: 5.15.9
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -18,7 +18,7 @@
     "@fontsource-variable/jost": "^5.2.6",
     "@fontsource-variable/playfair-display": "^5.2.6",
     "@iconify-json/ion": "^1.2.6",
-    "astro": "^5.13.5",
+    "astro": "^5.15.9",
     "fuse.js": "^7.1.0",
     "mdast-util-to-string": "^4.0.0",
     "reading-time": "^1.5.0",