script pp: Fix python 3.8 compatibility

For some reason `pd.Timestamp.utctimetuple()` raises a `TypeError` on
python 3.8., see pandas-dev/pandas#32174.

This functions is used internally by `pysolar`, which we use to
(re-)calculate the solar zenith angles for level-2 post processing.
Passing a `datetime.dateime` to the `pysolar` function fixes it for now.

Author: st-bender

scripts/scia_post_process_l2.py

@@ -366,7 +366,7 @@ def _read_gm(fname):
 		else:
 			sdd.noem_no[i][:] = np.nan
 		sdd.sza[i] = 90. - sun_alt_func(lat, sdd.lons[i],
-				dt.timedelta(np.asscalar(sdd.utcdays[i])) + dtrefdate,
+				(dt.timedelta(np.asscalar(sdd.utcdays[i])) + dtrefdate).to_pydatetime(),
 				elevation=mean_alt_m)
 	sdd.vmr = sdd.densities / sdd.dens_tot * 1.e9  # ppb
 	return dts_retr_interp0, time0, lst0, lon0, sdd