Use SSH agent for Github access for the updater workflow

Author: xuanyang15

.github/workflows/update-python-docs.yaml

@@ -38,11 +38,10 @@ jobs:
         with:
           credentials_json: '${{ secrets.ADK_GCP_SA_KEY }}'
 
-      - name: Configure Git Credentials
-        env:
-          PAT: ${{ secrets.ADK_BOT_GITHUB_TOKEN }}
-        run: |
-          git config --global url."https://oauth2:${PAT}@github.com/".insteadOf "https://github.com/"
+      - name: Load adk-bot SSH Private Key
+        uses: webfactory/ssh-agent@v0.9.0
+        with:
+          ssh-private-key: ${{ secrets.ADK_BOT_SSH_PRIVATE_KEY }}
 
       - name: Install dependencies
         run: |