Support Immutable GitHub Releases

[reidbaker]

As suggested by @jtmcdole in #158 (comment):
For another version:

• We can mark releases as immutable. GitHub will make the sha256 for us. Binaries cannot change.
• It means we upload all binaries in the release step like this:

      - name: Create Immutable GitHub Release
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          gh release create ${{ github.ref_name }} ./all-assets/* \
            --title "Release ${{ github.ref_name }}" \
            --generate-notes