Tendon imports in from_files_cfg had a typo that prevented importing.
This is resolved in this commit.

## Type of change

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

## Checklist

- [X] I have read and understood the [contribution
guidelines](https://isaac-sim.github.io/IsaacLab/main/source/refs/contributing.html)
- [X] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] 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
Signed-off-by: Kyle Morgenstein <34984693+KyleM73@users.noreply.github.com>