Fix test_pipelines_video_classification that was always failing

[CalOmnie]

What does this PR do?

tests/test_pipelines_video_classification.py was always failing because the output of the video classifier, when run with one file path (as opposed to a list), is returning a list[dict] whereas the testing code was expecting a list[list[dict]], this PR corrects that assumption.

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It would be nice if someone could check that pytest tests/test_pipelines_video_classification.py actually fails for them too, it is possible that the issue comes from my environment

[Rocketknight1]

cc @ydshieh, can you confirm this test was failing?