Fix select2 for newer django versions

[paris-ci]

  File "/Users/x/Desktop/WorkSpace/TSP/TSP-evaluations/questionnaires/models/misc.py", line 9, in <module>
    import select2.fields
  File "/Users/x/.pyenv/versions/3.12.2/lib/python3.12/site-packages/select2/fields.py", line 117, in <module>
    class Select2ModelFieldMixin(Select2FieldMixin):
  File "/Users/x/.pyenv/versions/3.12.2/lib/python3.12/site-packages/select2/fields.py", line 141, in Select2ModelFieldMixin
    choices = property(_get_choices, forms.ChoiceField._set_choices)
                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: type object 'ChoiceField' has no attribute '_set_choices'