Fix nightly test setup
# What does this PR do?

The nightly tests were not properly triggered because I made a typo in the variable name to set 🤦‍♂️ . This is fixed since yesterday., but now there is a failure in the setup (see [here](https://app.circleci.com/jobs/github/huggingface/transformers/597479?utm_campaign=workflow-failed&utm_medium=email&utm_source=notification)) because I forgot to checkout the repo.
_The documentation is not available anymore as the PR was closed or merged._