modify doc generation workflow

.github/workflows/doc.yml

@@ -59,14 +59,12 @@ jobs:
         with:
           repository: versotile-org/docs.versotile.org
           ssh-key: ${{ secrets.DOCS_DEPLOY_KEY }}
-          ref: docs
+          ref: main
 
       - name: Clean up docs directory
         run: |
-          cp {docs/,}index.html
+          git checkout docs
           rm -r docs/*
-          mv index.html docs/
-          cp CNAME docs/
 
       - name: Download `doc`
         uses: actions/download-artifact@v4
@@ -82,5 +80,6 @@ jobs:
       - name: Commit and push
         run: |
           git add docs
+          git checkout main docs/
           git commit -m ":rocket: update docs from \`verso\` repository"
           git push origin docs