Fixed #12724 - fieldset not saving on model

[snipe]

I'm honestly not sure how this ever worked. The field name itself is just wrong. @uberbrady am I missing something here? I know we livewire'd this up, but I'm not sure how this worked in the first place (which I know it did.)

[what-the-diff]

PR Summary

• Renaming of custom_fieldset The custom_fieldset was renamed to fieldset_id for better clarity.
• Handling fieldset_id in store method If a value is present for fieldset_id, the model's field set id will be assigned accordingly; otherwise, null is assigned.
• Updating fieldset_id in update method Default values are properly managed when updating fieldset_id, ensuring accuracy and consistency in the models.

[uberbrady]

I mean, this seems pretty straightforward? I f it actually, like, works, then I'm absolutely all for it. If it was me who missed this (and, yes, I'm the last person who had hands on this), then I'm happy to take the blame. I kinda understand your reticence, because, like, this should've already been working, and it'd be weird if it had somehow stopped working. But, regardless, seems like a fair set of changes and I will accept them.