address xarray FutureWarning: In a future version of xarray the default value for compat will change from compat='no_conflicts' to compat='override'.

[blaylockbk]

FutureWarning: In a future version of xarray the default value for compat will change from compat='no_conflicts' to compat='override'. This is likely to lead to different results when combining overlapping variables with the same name. To opt in to new defaults and get rid of these warnings now use `set_options(use_new_combine_kwarg_defaults=True) or set compat explicitly.
o = xr.merge([o, ds], **kwargs)