set nightly release to draft

Signed-off-by: Sunny Yip <sunny@kusari.dev>

.github/workflows/release.yaml

@@ -139,6 +139,7 @@ jobs:
     with:
       base64-subjects: "${{ needs.goreleaser.outputs.hashes }}"
       upload-assets: true
+      draft-release: ${{ contains( github.ref, 'nightly' ) && true || false }} 
 
   provenance-container:
     name: generate provenance for container