chore(deps): bump @tensorflow/tfjs from 4.13.0 to 4.21.0

Bumps [@tensorflow/tfjs](https://github.com/tensorflow/tfjs) from 4.13.0 to 4.21.0.
- [Release notes](https://github.com/tensorflow/tfjs/releases)
- [Changelog](https://github.com/tensorflow/tfjs/blob/master/cloudbuild-release.yml)
- [Commits](https://github.com/tensorflow/tfjs/commits)

---
updated-dependencies:
- dependency-name: "@tensorflow/tfjs"
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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