CI: add attestation

Author: tacaswell

.github/workflows/release.yml

@@ -55,5 +55,10 @@ jobs:
       - name: Print out packages
         run: ls dist
 
+      - name: Generate artifact attestation for sdist and wheel
+        uses: actions/attest-build-provenance@ef244123eb79f2f7a7e75d99086184180e6d0018  # v1.4.4
+        with:
+          subject-path: dist/cycler-*
+
       - name: Publish package distributions to PyPI
         uses: pypa/gh-action-pypi-publish@15c56dba361d8335944d31a2ecd17d700fc7bcbc  # v1.12.2