Validator should use pd.Timestamp for comparisons, not datetime.date

[krivard]

I found this in the Automation logs -- we should fix it soon so we don't end up with any nasty surprises at the next pandas update (I don't think we pin pandas versions):

/mnt/data2/indicators/runtime/covid_act_now/env/lib/python3.8/site-packages/delphi_utils/validator/dynamic.py:313: FutureWarning: Comparison of Timestamp with datetime.date is deprecated in order to match the standard library behavior.  In a future version these will be considered non-comparable.Use 'ts == pd.Timestamp(date)' or 'ts.date() == date' instead.
  if reference_api_df_max_date < reference_end_date: