Bump puppeteer from 13.5.0 to 21.0.3 in /src/backend

Bumps [puppeteer](https://github.com/puppeteer/puppeteer) from 13.5.0 to 21.0.3.
- [Release notes](https://github.com/puppeteer/puppeteer/releases)
- [Changelog](https://github.com/puppeteer/puppeteer/blob/main/release-please-config.json)
- [Commits](puppeteer/puppeteer@v13.5.0...puppeteer-v21.0.3)

---
updated-dependencies:
- dependency-name: puppeteer
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>