build(deps): bump koa from 2.15.4 to 2.16.1 in /demo/backend

Bumps [koa](https://github.com/koajs/koa) from 2.15.4 to 2.16.1.
- [Release notes](https://github.com/koajs/koa/releases)
- [Changelog](https://github.com/koajs/koa/blob/master/History.md)
- [Commits](koajs/koa@2.15.4...v2.16.1)

---
updated-dependencies:
- dependency-name: koa
  dependency-version: 2.16.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

demo/backend/package.json

@@ -20,7 +20,7 @@
     "@koa/cors": "^5.0.0",
     "@koa/router": "^13.1.0",
     "@prisma/client": "^6.3.1",
-    "koa": "^2.15.4",
+    "koa": "^2.16.1",
     "koa-body": "^6.0.1"
   },
   "prisma": {