Enhance export-docs workflow for PR branch tracking (#1656)

Updated checkout step to track the PR branch and modified fetch depth. Added a step to sync with existing PR branch if it exists.

Author: saudsami

.github/workflows/export-docs.yml

@@ -30,16 +30,31 @@ jobs:
           token: ${{ secrets.EXPORT_PAT }}
 
       # ----------------------------------------------------------------
-      # 2. Check out markdown-service into a sibling directory
+      # 2. Check out markdown-service and try to track the PR branch
       # ----------------------------------------------------------------
       - name: Check out markdown-service
         uses: actions/checkout@v4
         with:
           repository: AgoraIO/markdown-service
           token: ${{ secrets.EXPORT_PAT }}
           path: markdown-service
-          fetch-depth: 1
+          fetch-depth: 0 # Changed to 0 so we can find existing remote branches
 
+      # ----------------------------------------------------------------
+      # 2.5 Prepare branch to accumulate changes
+      # ----------------------------------------------------------------
+      - name: Sync with existing PR branch if it exists
+        working-directory: markdown-service
+        run: |
+          # Check if the automated branch already exists on the remote
+          if git show-ref --verify --quiet refs/remotes/origin/auto-export/latest; then
+            echo "Found existing PR branch. Fetching and checking it out to accumulate changes..."
+            git checkout auto-export/latest
+            git pull origin auto-export/latest
+          else
+            echo "No existing PR branch found. Starting fresh from main."
+          fi
+          
       # ----------------------------------------------------------------
       # 3. Fetch products.js from the private AgoraIO/Docs repo
       # ----------------------------------------------------------------
@@ -183,4 +198,4 @@ jobs:
       # ----------------------------------------------------------------
       - name: No changes to export
         if: steps.changes.outputs.changed == 'false'
-        run: echo "✅ No markdown files changed — no PR needed."
+        run: echo "✅ No markdown files changed — no PR needed."