Bump braces and firebase-admin in /functions/testapp/functions

Removes [braces](https://github.com/micromatch/braces). It's no longer used after updating ancestor dependency [firebase-admin](https://github.com/firebase/firebase-admin-node). These dependencies need to be updated together.


Removes `braces`

Updates `firebase-admin` from 5.10.0 to 12.1.1
- [Release notes](https://github.com/firebase/firebase-admin-node/releases)
- [Commits](firebase/firebase-admin-node@v5.10.0...v12.1.1)

---
updated-dependencies:
- dependency-name: braces
  dependency-type: indirect
- dependency-name: firebase-admin
  dependency-type: direct:production
...

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Author: dependabot[bot]