Numba deprecation warning in akmaev_adjustment

[brian-rose]

Lately we're getting warning messages like this on every import climlab:

/srv/conda/envs/notebook/lib/python3.10/site-packages/climlab/convection/akmaev_adjustment.py:142: NumbaDeprecationWarning: The 'nopython' keyword argument was not supplied to the 'numba.jit' decorator. The implicit default value for this argument is currently False, but it will be changed to True in Numba 0.59.0. See https://numba.readthedocs.io/en/stable/reference/deprecation.html#deprecation-of-object-mode-fall-back-behaviour-when-using-jit for details.
  Akmaev_adjustment = jit(signature_or_function=Akmaev_adjustment)

We'll need to take a look at this deprecation notice in the Numba docs and see what needs doing here.