feature-8832: Add option "Not sure yet" to attendee Form Yes/No questions (#8929)

Author: khangon

app/api/helpers/custom_forms.py

@@ -30,7 +30,7 @@ def get_schema(form_fields):
         elif field.type == 'number':
             field_type = marshmallow.fields.Float
         elif field.type == 'boolean':
-            field_type = marshmallow.fields.Boolean
+            field_type = marshmallow.fields.Str
         else:
             raise UnprocessableEntityError(
                 {'pointer': '/data/complex-field-values/' + field.identifier},