code crashes with newer pynauty version

The following code in `learning/learner/src/symmetries/exact.py`
```
def compute_nauty_certificate(nauty_graph: NautyGraph):
    return certificate(nauty_graph)
```
when I used v2.8.6 of pynauty but seems to work fine if I downgrade to v1.1.2.

I'm using ubuntu 22.04 and python3.10.12.