fix(unit tests): drop .btn-secondary from carousel play/pause buttons

[julien-deramond]

Description

This PR suggests changing the markup used to render the play/pause buttons in carousels' unit tests so that they use the same one as in https://boosted.orange.com/docs/5.3/components/carousel/#with-pauseplay-button:

<button type="button" class="btn btn-icon carousel-control-play-pause pause" data-bs-target="#carouselExamplePause" data-bs-play-text="Play Carousel" data-bs-pause-text="Pause Carousel" title="Pause Carousel">
  <span class="visually-hidden">Pause Carousel</span>
</button>

It basically means to drop the use of .btn-secondary.

Note: it'll help with the work in progress in #2223

Motivation & Context

Consistency between the carousels' markups.

Types of change

• Bug fix (non-breaking which fixes an issue)

Live previews

N/A

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[louismaximepiton]

It's not exactly the carousel's actual markup since the pause button is contained inside the carousel but I'm fine with the changes since it passes tests