chore(deps): bump tar and firebase-tools in /demo_backend/functions

Bumps [tar](https://github.com/isaacs/node-tar) to 7.5.10 and updates ancestor dependency [firebase-tools](https://github.com/firebase/firebase-tools). These dependencies need to be updated together.


Updates `tar` from 7.5.7 to 7.5.10
- [Release notes](https://github.com/isaacs/node-tar/releases)
- [Changelog](https://github.com/isaacs/node-tar/blob/main/CHANGELOG.md)
- [Commits](isaacs/node-tar@v7.5.7...v7.5.10)

Updates `firebase-tools` from 13.35.1 to 15.8.0
- [Release notes](https://github.com/firebase/firebase-tools/releases)
- [Changelog](https://github.com/firebase/firebase-tools/blob/main/CHANGELOG.md)
- [Commits](firebase/firebase-tools@v13.35.1...v15.8.0)

---
updated-dependencies:
- dependency-name: tar
  dependency-version: 7.5.10
  dependency-type: indirect
- dependency-name: firebase-tools
  dependency-version: 15.8.0
  dependency-type: direct:production
...

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Author: dependabot[bot]