Python climatology calculation not retaining attributes

[xylar]

In the new #917 analysis, we're seeing:

Traceback (most recent call last):
  File "/gpfs/fs1/home/ac.xylar/chrysalis/mambaforge/envs/test_mpas_analysis_py3.9/lib/python3.9/site-packages/mpas_analysis/shared/analysis_task.py", line 322, in run
    self.run_task()
  File "/gpfs/fs1/home/ac.xylar/chrysalis/mambaforge/envs/test_mpas_analysis_py3.9/lib/python3.9/site-packages/mpas_analysis/ocean/histogram.py", line 539, in run_task
    xLabel = f"{ds[var_name].attrs['long_name']} " \
KeyError: 'long_name'

when we're not using ncclimo.