Fix nightly runs
# What does this PR do?

The pipeline that runs the nightly tests exits with `Unexpected argument(s): nightly` instead of running all tests. I think we just need to add it in the custom config as an argument (unused) so circleCI doesn't complain anymore.

Manually triggered the tests on this branch with `nightly` at `true` and it ran all tests (see workflow nightly in the tests).
_The documentation is not available anymore as the PR was closed or merged._