Update sphinx-build.yml

Make sure deleted files are no longer being served

.github/workflows/sphinx-build.yml

@@ -42,8 +42,9 @@ jobs:
       - name: Commit documentation changes
         run: |
           git clone https://github.com/open-ephys/acq-board-docs.git --branch gh-pages --single-branch gh-pages
-          cp -r docs/html/* gh-pages/
           cd gh-pages
+          rm -rf *
+          cp -r ../docs/html/* .
           git config --local user.email "[email protected]"
           git config --local user.name "GitHub Action"
           git add .