Update sitemaps.yml to use gh-pages branch (#28)

Author: glenn-jocher

.github/workflows/sitemaps.yml

@@ -19,6 +19,7 @@ jobs:
       - name: Checkout Repo
         uses: actions/checkout@v4
         with:
+          ref: gh-pages  # checkout gh-pages branch
           fetch-depth: 2  # fetch the current and previous commit
 
       - name: Set up Python