Tests: Add tests for playlist shortcode script loading for first invalid playlist

[Adi-ty]

Trac ticket: #63583

Patch Used: #9003

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Description

Added a unit test for wp_playlist_shortcode to ensure that playlist scripts are loaded when a valid playlist follows an invalid one.

Testing Instructions

Run the following command to verify the tests:

npm run test:php -- --filter=Tests_Media_Wp_Playlist_Shortcode 

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Props iamadisingh, abcd95, justlevine.

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[justlevine]

I only took a click glance but can we reuse the static $instance, seems to be the equivalent of $instance > 1

I know the stakes are low for a shortcode, but anything to avoid this antipattern leaking into more places.

[Adi-ty]

Hey @justlevine,
Thanks for the review.

I have tried reusing the static $instance. Using $instance >= 1 can work, but it will trigger the action for every valid playlist after the first shortcode. Using a static $is_loaded variable ensures the action is only triggered once, for the first valid playlist.

Let me know if you have further thoughts!

[TimothyBJacobs]

Merged in f40b60d.