zero_shot_object_detection ValueError fix for python 3.13

[AnkitAhlawat7742]

What does this PR do?

Python 3.13's doctest parser enforces stricter syntax validation. The closing )[0] is placed on a ... continuation line, which is no longer accepted so this PR fixes the malformed doctest by splitting the indexing into a separate statement, making it compatible with Python 3.13's parser while keeping the same behavior.

Fixes #45657

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Who can review?

Documentation: @stevhliu

[Rocketknight1]

LGTM!

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