[Test] Update vizro ai integration test for dataclass output

[Anna-Xiong]

Description

Update vizro-ai integration test to use customized output PlotOutputs dataclass.

• _return_all_text private attributes is no longer needed and the output dictionary will be replaced by dataclass
  for more details about the new feature please see [Feat] get vizro ai customized text output #488

Screenshot

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[maxschulz-COL]

LGTM! Does @l0uden need to change something for tests that are in the QA repo?