ci: Use GITHUB_OUTPUT envvar instead of set-output command (#276)

`save-state` and `set-output` commands used in GitHub Actions are deprecated and [GitHub recommends using environment files](https://github.blog/changelog/2023-07-24-github-actions-update-on-save-state-and-set-output-commands/).

This PR updates the usage of `set-output` to `$GITHUB_OUTPUT`

Instructions for envvar usage from GitHub docs:

https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter

Co-authored-by: Wei Li <[email protected]>

.github/workflows/build_pypi.yml

@@ -56,7 +56,7 @@ jobs:
       run: |
         if [[ "${{ github.event_name }}" == "push" ]] && \
            [[ "${{ github.event.ref }}" =~ ^refs/tags/v[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
-            echo ::set-output name=match::true
+            echo "match=true" >> $GITHUB_OUTPUT
         fi
 
     - name: Upload to PyPI