Make UnionTagNotFound error include expected_tags like it is done for UnionTagInvalid

[ragne]

Hey, no sure if this a correct place to ask for the enchantments, but is it possible to add expected_tags to the UnionTagNotFound like it's done with UnionTagInvalid?

What I wanted to achieve is to have that info in the ValidationError that is raised by pydantic so I can construct error messages like Unable to extract tag using discriminator 't'. Valid values are: ${values} for all models that exist in my project. Right now it's possible for union_tag_invalid error, but for union_tag_not_found there's no such fields.

I could work on that if this enchantment is even possible to do :)