Questions about getting repeatable results while using RANSAC for global registration

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

Hello! When using RANSAC for global registration, I found that the results were not stable. I also added `o3d.utility.random.seed(1)` before registration, but the results were still not stable. Would it be possible to get the same results when repeating RANSAC?