fix: Use .zip in archive path

Fixes dart-lang#118

Ensures that downloads of the Dart SDK zip file carry the `.zip` extension so that subsequent calls to `Expand-Archive` on Windows succeed.

## Notes

- Uses Dart `3.3.0-16.0.dev`. The current version (`3.3.0-5.0.dev`) is not published so I kept it to the closest published version.
- The diff of `index.mjs` is quite large. I believe this is due to the version of Node I'm using (`20.7.0`). Happy to use a different version to keep the diff small, but wasn't sure which one is currently used.

Author: dnys1