Fix .shape on dataset in unit test

tests/test_model.py

@@ -688,7 +688,7 @@ def test_forecasting_model_predict_return_valid_times(self):
                 # Check we can compute errors using the valid time coord ('time')
                 errors = pred_var["mean"] - self.da.sel(time=pred_var.time)
                 assert errors.dims == ("lead_time", "init_time", "x1", "x2")
-                assert errors.shape == pred_var.shape
+                assert errors.shape == pred_var["mean"].shape
             elif isinstance(pred_var, pd.DataFrame):
                 # Makes coordinate checking easier by avoiding repeat values
                 pred_var = pred_var.to_xarray().isel(x1=0, x2=0)