build(deps): bump github.com/google/go-jsonnet in /scripts

Bumps [github.com/google/go-jsonnet](https://github.com/google/go-jsonnet) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/google/go-jsonnet/releases)
- [Changelog](https://github.com/google/go-jsonnet/blob/master/.goreleaser.yml)
- [Commits](https://github.com/google/go-jsonnet/compare/v0.20.0...v0.21.0

)

---
updated-dependencies:
- dependency-name: github.com/google/go-jsonnet
  dependency-version: 0.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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