Bump actions/attest-build-provenance from 2.0.1 to 2.1.0

Bumps [actions/attest-build-provenance](https://github.com/actions/attest-build-provenance) from 2.0.1 to 2.1.0.
- [Release notes](https://github.com/actions/attest-build-provenance/releases)
- [Changelog](https://github.com/actions/attest-build-provenance/blob/main/RELEASE.md)
- [Commits](actions/attest-build-provenance@v2.0.1...v2.1.0)

---
updated-dependencies:
- dependency-name: actions/attest-build-provenance
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

.github/workflows/release.yml

@@ -32,7 +32,7 @@ jobs:
         run: |
           ./cake upload
       - name: Attest packages
-        uses: actions/attest-build-provenance@v2.0.1
+        uses: actions/attest-build-provenance@v2.1.0
         with:
           subject-path: out/pkg/release/*.nupkg
       - name: Upload artifacts