Fix placing 'index' column in line and trafo

Signed-off-by: furqan463 <[email protected]>

Author: furqan463

src/power_grid_model_io/converters/pandapower_converter.py

@@ -2430,7 +2430,7 @@ def get_switch_states(self, pp_table: str) -> pd.DataFrame:
         else:
             raise KeyError(f"Can't get switch states for {pp_table}")
 
-        component = self.pp_input_data[pp_table]
+        component = self.pp_input_data[pp_table].copy()
         component["index"] = component.index
 
         # Select the appropriate switches and columns