use new deploy key

.github/workflows/docs.yml

@@ -34,7 +34,7 @@ jobs:
           # Create .nojekyll file to prevent GitHub Pages from ignoring files that begin with an underscore
           touch _build/html/.nojekyll
 
-      - name: Deploy to GitHub Pages
+      - name: Deploy to GitHub Pages (Main Branch)
         if: github.event_name == 'push' && github.ref == 'refs/heads/main'
         uses: peaceiris/actions-gh-pages@v3
         with:
@@ -44,14 +44,22 @@ jobs:
           enable_jekyll: false
           full_commit_message: ${{ github.event.head_commit.message }}
 
+      - name: Setup SSH for PR Previews
+        if: github.event_name == 'pull_request'
+        run: |
+          mkdir -p ~/.ssh
+          echo "${{ secrets.GH_PAGES_DEPLOY_KEY }}" > ~/.ssh/id_rsa
+          chmod 600 ~/.ssh/id_rsa
+          ssh-keyscan github.com >> ~/.ssh/known_hosts
+
       - name: Deploy Preview for PRs
         if: github.event_name == 'pull_request'
         uses: peaceiris/actions-gh-pages@v3
         with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
+          deploy_key: ${{ secrets.GH_PAGES_DEPLOY_KEY }}
           publish_dir: ./docs/_build/html
           destination_dir: pr-previews/${{ github.event.number }}
-          external_repository: ${{ github.repository }}
+          external_repository: MHKiT-Software/MHKiT
           keep_files: true
           enable_jekyll: false
           full_commit_message: ${{ github.event.head_commit.message }}