[4.0] Remove margin between accordion slides

[SharkyKZ]

Fixes #29311.

Summary of Changes

Removes margin between Bootstrap accordion slides.

Testing Instructions

Edit a module in frontend.

Expected result

Looks OK.

Actual result

Gap between slides and first slide is missing the bottom border:

Documentation Changes Required

No.

[infograf768]

I have a B/C problem here with com_localise after this patch.
I do use the below code and display a table in the slide

<?php echo HTMLHelper::_('bootstrap.startAccordion', 'slide-translations', array('active' => '')); ?>
<?php echo HTMLHelper::_('bootstrap.addSlide', 'slide-translations', Text::_('COM_LOCALISE_SLIDER_TRANSLATIONS_LEGEND'), 'legend'); ?>

Then I have another accordeon + slide.
I lose the mb-2 margin

.mb-2, .my-2 {
    margin-bottom: 0.5rem !important;
}

Before this PR

After this PR

[infograf768]

I can evidently solve it by adding the mb-2 class to the div enclosing this template but I wonder if this PR is the correct solution.

		<div class="col-md-12 mb-2">
			<?php echo $this->loadTemplate('legend'); ?>
		</div>

[ceford]

I have tested this item ✅ successfully on 878e3bc

First bottom margin present - but no gaps between unopened tabs, is that intended.

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[infograf768]

I have tested this item ✅ successfully on 878e3bc

I guess will just have to modify my component.

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[infograf768]

rtc

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[richard67]

Thanks all!

[SharkyKZ]

@ceford Yes, that's expected.

@infograf768 you can also pass mb-2 class to HTMLHelper::_('bootstrap.addSlide').

This PR is fine in that it fixes the default styling. Before patch, this looked fine in Atum because it has custom CSS but not in Cassiopeia or in any stock Bootstrap template.