Fixes example in migration docs (#708)

# Description

Fixes inaccuracy in migration docs.
Now the docs correspond to the actual code.

Fixes #706

## Type of change

- This change requires a documentation update

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] 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

docs/source/migration/migrating_from_isaacgymenvs.rst

@@ -782,7 +782,7 @@ The ``progress_buf`` variable has also been renamed to ``episode_length_buf``.
 |     velocities = 0.5 * (torch.rand((len(env_ids), self.num_dof),      |                                                                           |
 |         device=self.device) - 0.5)                                    |     time_out = self.episode_length_buf >= self.max_episode_length - 1     |
 |                                                                       |     out_of_bounds = torch.any(torch.abs(                                  |
-|     self.dof_pos[env_ids, :] = positions[:]                           |         self.joint_pos[:, self._pole_dof_idx] > self.cfg.max_cart_pos),   |
+|     self.dof_pos[env_ids, :] = positions[:]                           |         self.joint_pos[:, self._cart_dof_idx]) > self.cfg.max_cart_pos,   |
 |     self.dof_vel[env_ids, :] = velocities[:]                          |         dim=1)                                                            |
 |                                                                       |     out_of_bounds = out_of_bounds | torch.any(                            |
 |     env_ids_int32 = env_ids.to(dtype=torch.int32)                     |         torch.abs(self.joint_pos[:, self._pole_dof_idx]) > math.pi / 2,   |

docs/source/migration/migrating_from_omniisaacgymenvs.rst

@@ -706,7 +706,7 @@ reset the ``episode_length_buf`` buffer.
 |   resets = torch.where(                                          |                                                                          |
 |     torch.abs(self.pole_pos) > math.pi / 2, 1, resets)           |     time_out = self.episode_length_buf >= self.max_episode_length - 1    |
 |   resets = torch.where(                                          |     out_of_bounds = torch.any(torch.abs(                                 |
-|     self.progress_buf >= self._max_episode_length, 1, resets)    |         self.joint_pos[:, self._pole_dof_idx] > self.cfg.max_cart_pos),  |
+|     self.progress_buf >= self._max_episode_length, 1, resets)    |         self.joint_pos[:, self._cart_dof_idx]) > self.cfg.max_cart_pos,  |
 |   self.reset_buf[:] = resets                                     |         dim=1)                                                           |
 |                                                                  |     out_of_bounds = out_of_bounds | torch.any(                           |
 |                                                                  |         torch.abs(self.joint_pos[:, self._pole_dof_idx]) > math.pi / 2,  |