CI Tests are broken in 3.12

[awgymer]

Description of the bug

CI tests are failing under Python 3.12 with errors like:

 AttributeError: 'called_once_with' is not a valid assertion. Use a spec for the mock if 'called_once_with' is meant to be an attribute.. Did you mean: 'assert_called_once_with'?

This is due to changes made to the unittest behaviour (which I couldn't see listed anywhere in the official docs so...)

For a full explanation of the goings on please see: python/cpython#100690

Command used and terminal output

No response

System information

No response

[mirpedrol]

Done with #2891, thanks!