Prune history of gh-pages branch

This will prune the git history and allow easier navigation using git
log --graph et al

Author: ch1bo

.github/workflows/ci.yml

@@ -865,4 +865,5 @@ jobs:
         uses: peaceiris/actions-gh-pages@v3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN || github.token }}
-          publish_dir: ./github-pages
+          publish_dir: ./github-pages
+          force_orphan: true