MESMER-M minor issue with harmonic model

[sarasita]

Function fit_harmonic_model does not throw an error when calling it with predictor and target data that does not have the same spatial structure (e.g. calling it with tas_globmean as predictor). I'd suggest to add

def fit_harmonic_model(..., gridcell_dim = 'gridcell')
and

if not len(monthly_target[gridcell_dim]) == len(yearly_predictor[gridcell_dim]):
raise ValueError("Yearly predictor values and monthly target data must have the same number of gridcells")

And there is also v minor error in the function description, I think it should be:

monthly_target : xr.DataArray of shape (n_months*n_years, n_gridcells)