Check potential issue with ignored forced dtypes in `json_ai_from_problem`

[paxcema]

As reported by @pafluxa

[paxcema]

Closing. Cannot reproduce, override works fine:

pdef = ProblemDefinition.from_dict({"target": target, 'dtype_dict': {'$col': '$type'})
json_ai = json_ai_from_problem(df, problem_definition=pdef)