add blank line to meet pep8 standard

observation_sim/sim_steps/add_objects.py

@@ -10,6 +10,7 @@ from observation_sim.psf import PSFGauss, FieldDistortion, PSFInterp, PSFInterpS
 from astropy.time import Time
 from datetime import datetime, timezone
 
+
 def _is_obj_valid(self, obj):
     if obj.param['star'] == 4:
         # Currently there's no parameter checks for 'calib' type