Bump next from 9.4.2 to 13.5.0 in /frontend/plan

Bumps [next](https://github.com/vercel/next.js) from 9.4.2 to 13.5.0.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v9.4.2...v13.5.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

frontend/plan/package.json

@@ -30,7 +30,7 @@
     "express": "^4.17.1",
     "http-proxy-middleware": "^1.0.4",
     "ics": "^2.37.0",
-    "next": "9.4.2",
+    "next": "13.5.0",
     "next-transpile-modules": "^3.3.0",
     "pcx-shared-components": "0.1.0",
     "polished": "^3.6.6",