Fix doc PRs preview generation (#28)

Clone the PR branch not main

Author: sebastienvermeille

.github/workflows/pushpreview.yml

@@ -15,6 +15,8 @@ jobs:
       contents: read        # Default for reading the repository contents
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          ref: ${{ github.head_ref }}
       - name: Comment
         run: |
           gh pr comment ${{ github.event.pull_request.number }} --repo ${{ github.repository }} --body "⚙️ Hang tight! PushPreview is currently building your preview. We'll share the URL as soon as it's ready."