Bump zod and next

Removes [zod](https://github.com/colinhacks/zod). It's no longer used after updating ancestor dependency [next](https://github.com/vercel/next.js). These dependencies need to be updated together.


Removes `zod`

Updates `next` from 13.4.9 to 13.5.4
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](https://github.com/vercel/next.js/compare/v13.4.9...v13.5.4)

---
updated-dependencies:
- dependency-name: zod
  dependency-type: indirect
- dependency-name: next
  dependency-type: direct:production
...

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

package.json

@@ -22,7 +22,7 @@
     "gray-matter": "^4.0.2",
     "image-size": "1.0.0",
     "mdx-bundler": "^8.0.0",
-    "next": "^13.4.6",
+    "next": "^13.5.4",
     "next-themes": "^0.0.14",
     "postcss": "^8.4.31",
     "preact": "^10.6.2",