Replace use of deprecated ::set-output

See https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

Author: mattt

.github/workflows/ci.yml

@@ -45,7 +45,7 @@ jobs:
       - name: Build tarball
         id: pack
         run: |
-          echo "::set-output name=tarball-name::$(npm --loglevel error pack)"
+          echo "tarball-name=$(npm --loglevel error pack)" >> $GITHUB_OUTPUT
       - uses: actions/upload-artifact@v3
         with:
           name: package-tarball