message: actions: remove unused var
  If .github/workflows/release.yml the cnt is not used.
diff: @@ -193,8 +193,7 @@ jobs:
  - name: prepare release env
  run: |
  echo "tarballs<<EOF" >> $GITHUB_ENV
  - cnt=0
  - for I in $(ls nydus-tarball);do cnt=$((cnt+1)); echo "nydus-tarball/${I}" >> $GITHUB_ENV; done
  + for I in $(ls nydus-tarball);do echo "nydus-tarball/${I}" >> $GITHUB_ENV; done
  echo "EOF" >> $GITHUB_ENV
  tag=$(echo $GITHUB_REF | cut -d/ -f3-)
  echo "tag=${tag}" >> $GITHUB_ENV
  