Use zip from flake in CI

Author: john-shaffer

.github/workflows/build.yml

@@ -31,7 +31,8 @@ jobs:
 
       - name: Build plugin zip
         run: |
-          nix develop -c bash tools/build_release.sh plugin
+          nix build .#wp2static
+          cp result/wp2static.zip plugin.zip
 
       - name: Create GitHub Release
         if: startsWith(github.ref, 'refs/tags/v')