Fixes event term for pushing root by setting velocity (#1584)

# Description

Previously, the event term set the current root velocity to the sampled
values. However, this isn't the same as "pushing" the root. This MR
fixes this issue by changing the operation inside.

## Type of change

- New feature (non-breaking change which adds functionality)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

source/extensions/omni.isaac.lab/omni/isaac/lab/envs/mdp/events.py

@@ -628,7 +628,7 @@ def push_by_setting_velocity(
     # sample random velocities
     range_list = [velocity_range.get(key, (0.0, 0.0)) for key in ["x", "y", "z", "roll", "pitch", "yaw"]]
     ranges = torch.tensor(range_list, device=asset.device)
-    vel_w[:] = math_utils.sample_uniform(ranges[:, 0], ranges[:, 1], vel_w.shape, device=asset.device)
+    vel_w += math_utils.sample_uniform(ranges[:, 0], ranges[:, 1], vel_w.shape, device=asset.device)
     # set the velocities into the physics simulation
     asset.write_root_com_velocity_to_sim(vel_w, env_ids=env_ids)