Copy GitHub deploy result to non-symlink dir

deploy-pages@v4 complains if anything is a symlink. `nix build`
creates `result` which is a symlink into the `/nix/store`.

.github/workflows/gh-pages.yml

@@ -30,10 +30,12 @@ jobs:
        extra_nix_config: experimental-features = nix-command flakes
     - uses: DeterminateSystems/magic-nix-cache-action@v4
     - run: nix build
+    - run: mkdir github-pages
+    - run: cp -r ./result/* ./github-pages
     - uses: actions/upload-artifact@v4
       with:
         name: github-pages
-        path: result
+        path: github-pages
 
   deploy:
     environment: