Fix action indexing in the action manager (#23)

# Description

Fixes action indexing for multiple actions. Currently all successive
actions mimic the first one due to an indexing error.

## Type of change

- Bug fix (non-breaking change which fixes an issue)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] 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.orbit/omni/isaac/orbit/managers/action_manager.py

@@ -224,6 +224,7 @@ class ActionManager(ManagerBase):
         for term in self._terms:
             term_actions = action[:, idx : idx + term.action_dim]
             term.process_actions(term_actions)
+            idx += term.action_dim
 
     def apply_action(self) -> None:
         """Applies the actions to the environment/simulation.