actions: set explicit git username and email (#139)

Right now, commits are being attributed to me:
https://github.com/twitter/opensource-website/commits/gh-pages

This will hopefully fix that.

Author: willnorris

.github/workflows/github-pages.yml

@@ -33,5 +33,7 @@ jobs:
         uses: peaceiris/actions-gh-pages@bbdfb200618d235585ad98e965f4aafc39b4c501 # v3.7.3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
+          user_name: twitter-service
+          user_email: <[email protected]>
           publish_dir: ./public
           cname: opensource.twitter.dev