handle headless state in git pull

.github/workflows/build-docs.yml

@@ -77,11 +77,13 @@ jobs:
           fetch-depth: 1
           path: modal/examples
 
-      - name: Set examples remote to HTTPS
+      - name: Set up git environment for pull in invoke task
         working-directory: modal/examples
         run: |
           git remote set-url origin https://github.com/modal-labs/modal-examples.git
-
+          branch_name="${GITHUB_REF#refs/heads/}"
+          git fetch origin $branch_name
+          git checkout $branch_name
 
       - name: Build the docs
         working-directory: modal