XspectraCrystalWorkChain: Fix Input Bugs

Fixes two bugs in the input steps of the `XspectraCrystalWorkChain`:
* `WorkChain`s except when using `xch_smear` because the step to remove
  instances of `starting_magnetization(` was `pop`ing keys from the
dictionary which it was looping over.
* The `abs_atom_marker` input was not being passed to
  `get_xspectra_structures` correctly due to a typo.

src/aiida_quantumespresso/workflows/xspectra/crystal.py

@@ -523,7 +523,7 @@ def get_xspectra_structures(self):
 
         inputs = {
             'absorbing_elements_list' : elements_list,
-            'absorbing_atom_marker' : self.inputs.abs_atom_marker,
+            'abs_atom_marker' : self.inputs.abs_atom_marker,
             'metadata' : {
                 'call_link_label' : 'get_xspectra_structures'
             }
@@ -686,7 +686,9 @@ def run_all_xspectra_core(self): # pylint: disable=too-many-statements
                 new_scf_params['SYSTEM']['starting_magnetization'] = {abs_atom_marker : 1}
 
             # remove any duplicates created from the "core_hole_treatments.yaml" defaults
-            for key in new_scf_params['SYSTEM'].keys():
+            # new_scf_params_keys = [k for k in new_scf_params['SYSTEM'].keys()]
+            new_scf_params_keys = list(new_scf_params['SYSTEM'].keys())
+            for key in new_scf_params_keys:
                 if 'starting_magnetization(' in key:
                     new_scf_params['SYSTEM'].pop(key, None)