build(deps): bump github.com/sigstore/rekor

Bumps [github.com/sigstore/rekor](https://github.com/sigstore/rekor) from 0.12.1-0.20220915152154-4bb6f441c1b2 to 1.2.0.
- [Release notes](https://github.com/sigstore/rekor/releases)
- [Changelog](https://github.com/sigstore/rekor/blob/main/CHANGELOG.md)
- [Commits](https://github.com/sigstore/rekor/commits/v1.2.0)

---
updated-dependencies:
- dependency-name: github.com/sigstore/rekor
  dependency-type: indirect
...

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