feat(deps): bump github.com/sigstore/sigstore from 1.8.8 to 1.8.9 (#169)

Bumps [github.com/sigstore/sigstore](https://github.com/sigstore/sigstore) from 1.8.8 to 1.8.9.
- [Release notes](https://github.com/sigstore/sigstore/releases)
- [Commits](https://github.com/sigstore/sigstore/compare/v1.8.8...v1.8.9)

---
updated-dependencies:
- dependency-name: github.com/sigstore/sigstore
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

go.mod

@@ -18,7 +18,7 @@ require (
 	github.com/secure-systems-lab/go-securesystemslib v0.8.0
 	github.com/sigstore/cosign/v2 v2.4.0
 	github.com/sigstore/rekor v1.3.6
-	github.com/sigstore/sigstore v1.8.8
+	github.com/sigstore/sigstore v1.8.9
 	github.com/sigstore/sigstore/pkg/signature/kms/aws v1.8.9
 	github.com/sigstore/sigstore/pkg/signature/kms/gcp v1.8.9
 	github.com/stretchr/testify v1.9.0