Readthedocs: Don't let notebook failures pass silently (projectmesa#2276

)

Adds both to conf.py:

nb_execution_allow_errors = False
nb_execution_raise_on_error = True

To make sure that when one of the (tutorial) notebooks fails, the Readthedocs also fails and doesn't continue silently.

See https://myst-nb.readthedocs.io/en/latest/computation/execute.html#error-reporting-warning-vs-failure