Use isinstance instead of checking type equality (#1459)

Author: matt-graham

src/tlo/analysis/utils.py

@@ -290,7 +290,9 @@ def generate_series(dataframe: pd.DataFrame) -> pd.Series:
             try:
                 df: pd.DataFrame = load_pickled_dataframes(results_folder, draw, run, module)[module][key]
                 output_from_eval: pd.Series = generate_series(df)
-                assert pd.Series == type(output_from_eval), 'Custom command does not generate a pd.Series'
+                assert isinstance(output_from_eval, pd.Series), (
+                    'Custom command does not generate a pd.Series'
+                )
                 if do_scaling:
                     res[draw_run] = output_from_eval * get_multiplier(draw, run)
                 else: