FIX: update nb sync to main (#195)

Author: mmcky

.github/workflows/publish.yml

@@ -91,13 +91,14 @@ jobs:
           cp _build/jupyter/*.ipynb _build/lecture-python-advanced.notebooks
           ls -a _build/lecture-python-advanced.notebooks
       - name: Commit latest notebooks to lecture-python-advanced.notebooks
-        uses: cpina/github-action-push-to-another-repository@master
+        uses: cpina/github-action-push-to-another-repository
         env:
           API_TOKEN_GITHUB: ${{ secrets.QUANTECON_SERVICES_PAT }}
         with:
           source-directory: '_build/lecture-python-advanced.notebooks/'
           destination-repository-username: 'QuantEcon'
           destination-repository-name: 'lecture-python-advanced.notebooks'
+          target-branch: 'main'
           commit-message: 'auto publishing updates to notebooks'
           destination-github-username: 'quantecon-services'
           user-email: [email protected]