fix: fetch latest main before creating blog post branch

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: tianzhou

.github/workflows/weekly-blog-post.yml

@@ -54,7 +54,8 @@ jobs:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
           BRANCH="blog/weekly-$(date +%Y-%m-%d)"
-          git checkout -b "$BRANCH"
+          git fetch origin main
+          git checkout -b "$BRANCH" origin/main
           git add website/content/blog/
           git config user.name "github-actions[bot]"
           git config user.email "github-actions[bot]@users.noreply.github.com"