Bump @sigstore/core from 3.1.0 to 3.2.1 in /frontend

Bumps [@sigstore/core](https://github.com/sigstore/sigstore-js) from 3.1.0 to 3.2.1.
- [Release notes](https://github.com/sigstore/sigstore-js/releases)
- [Commits](https://github.com/sigstore/sigstore-js/compare/sigstore@3.1.0...@sigstore/core@3.2.1)

---
updated-dependencies:
- dependency-name: "@sigstore/core"
  dependency-version: 3.2.1
  dependency-type: indirect
...

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Author: dependabot[bot]