Fixes: #17796 Custom Field Choices -> Create & Add Another causes IndexError

[renatoalmeidaoliveira]

Fixes: #17796 Custom Field Choices -> Create & Add Another causes IndexError

• In the current release this issue doesn't raises an Exception, but setups a wrong vaule to the form after clicking in Create & Add Another
• The fix consists in convert the array query into a string to fit the Form field that is an CharField
• It should be possible to change the behaiviour of prepare_cloned_fields, but IMO that may lead to unwanted collateral effects, and its leads to a more complex solution

[arthanson]

@renatoalmeidaoliveira This fixes the issue and works, but I'm a bit uncomfortable with the code, it seems like this is patching the symptom rather than the initial problem. When we do the add-another it looks like it is getting sent in as a stringified tuple and your code here is deconstructing it. Can we look at why the add-another code is passing it in like this and can it just be made to pass it in the same as the edit case? I want to make sure we understand why this is different in the fist-place - if it can't be fixed there then can you please add a description in the PR why it is being passed in differently.

[renatoalmeidaoliveira]

@arthanson I think the "real" problem relies in the different field type between the form and the model.
The CustomFieldChoiceSetForm uses a CharField for the extra_choices fields code
While the CustomFieldChoiceSet model uses an ArrayField type for extra_choices code
Because of the type difference there must be some kind of patch that convert those types.