Fix unresolved reference (#4722)

The variable `species` was an unresolved reference and needed to accessed via
`self.species` instead.

Fixed also a word `specie` where `species` was meant.

Python/pywarpx/picmi.py

@@ -2469,7 +2469,7 @@ def diagnostic_initialize_inputs(self):
         if self.species is None:
             species_names = pywarpx.particles.species_names
         elif np.iterable(self.species):
-            species_names = [specie.name for specie in self.species]
+            species_names = [species.name for species in self.species]
         else:
             species_names = [self.species.name]
 
@@ -2696,9 +2696,9 @@ def diagnostic_initialize_inputs(self):
         if self.species is None:
             species_names = pywarpx.particles.species_names
         elif np.iterable(self.species):
-            species_names = [specie.name for specie in self.species]
+            species_names = [species.name for species in self.species]
         else:
-            species_names = [species.name]
+            species_names = [self.species.name]
 
         for name in species_names:
             diag = pywarpx.Bucket.Bucket(self.name + '.' + name,