Attempt at fixing publish step (#2898)

Summary:
Uses a custom GITHUB_PUBLISH_TOKEN with push permissions instead of the default provided GITHUB_TOKEN that cannot push to protected branches.
Pull Request resolved: #2898

Test Plan: Let's see if this fixes the publish...

Differential Revision: D18072386

fbshipit-source-id: dc9eea784977dbc1c00922e6f000e467b9b02e21

.github/workflows/docusaurus.yml

@@ -27,5 +27,5 @@ jobs:
         run: |
           git config --global user.email "relay-bot@users.noreply.github.com"
           git config --global user.name "Relay Bot"
-          echo "machine github.com login relay-bot password ${{secrets.GITHUB_TOKEN}}" > ~/.netrc
+          echo "machine github.com login relay-bot password ${{secrets.GITHUB_PUSH_TOKEN}}" > ~/.netrc
           ORGANIZATION_NAME=$(dirname $GITHUB_REPOSITORY) GIT_USER=relay-bot yarn run publish-gh-pages