ci: bump actions/attest-build-provenance from 2 to 3

Bumps [actions/attest-build-provenance](https://github.com/actions/attest-build-provenance) from 2 to 3.
- [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...v3)

---
updated-dependencies:
- dependency-name: actions/attest-build-provenance
  dependency-version: '3'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/cd.yml

@@ -73,7 +73,7 @@ jobs:
 
       - name: Attest
         if: startsWith(github.ref, 'refs/tags/v')
-        uses: actions/attest-build-provenance@v2
+        uses: actions/attest-build-provenance@v3
         with:
           subject-path: "${{ github.workspace }}/dist/**/mercure"