Migrate set-output to $GITHUB_OUTPUT (#24)

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

Author: tanakakc

.github/workflows/test.yml

@@ -26,7 +26,7 @@ jobs:
       run: |
         git fetch --force --no-tags origin 'refs/tags/v*:refs/tags/v*'
         bundle exec rake build
-        echo "::set-output name=pkg::${GITHUB_REPOSITORY#*/}-${RUNNING_OS%-*}"
+        echo "pkg=${GITHUB_REPOSITORY#*/}-${RUNNING_OS%-*}" >> $GITHUB_OUTPUT
       env:
         RUNNING_OS: ${{matrix.os}}
       if: ${{ matrix.ruby == '3.1' && !startsWith(matrix.os, 'ubuntu') }}