refactor: remove artifact attestation step from nightly build workflow

.github/workflows/nightly.yml

@@ -115,10 +115,3 @@ jobs:
             linux/arm64/v8
           cache-from: type=gha
           cache-to: type=gha,mode=max
-
-      - name: Generate artifact attestation
-        uses: actions/attest-build-provenance@v1
-        with:
-          subject-name: ${{ env.IMAGE_NAME }}
-          subject-digest: ${{ steps.build.outputs.digest }}
-          push-to-registry: true