Bump koa from 2.15.3 to 2.15.4 in /backend/packages/Upgrade (#2217)

Bumps [koa](https://github.com/koajs/koa) from 2.15.3 to 2.15.4.
- [Release notes](https://github.com/koajs/koa/releases)
- [Changelog](https://github.com/koajs/koa/blob/2.15.4/History.md)
- [Commits](koajs/koa@2.15.3...2.15.4)

---
updated-dependencies:
- dependency-name: koa
  dependency-type: indirect
...

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