[4.0] Fix Alert multiple error display

[infograf768]

Pull Request for Issue #30391

Summary of Changes

Installation Alerts are using the js. The <div> was misplaced.
I added a class but it is not necessary when using default core Installation.

Testing Instructions

Install a clean Joomla using a superuser password shorter than 12 characters

Patch, use NPM CI and install again

EDIT: To test multiple alerts in backend, add in Atum index.php

Factory::getApplication()->enqueueMessage('error message','error');
Factory::getApplication()->enqueueMessage('another long error message','error');
Factory::getApplication()->enqueueMessage('another very long error message','error');
Factory::getApplication()->enqueueMessage('warning message','warning');
Factory::getApplication()->enqueueMessage('warning message','warning');
Factory::getApplication()->enqueueMessage('notice message','notice');

Actual result BEFORE applying this Pull Request

Expected result AFTER applying this Pull Request

@brianteeman @chmst

[brianteeman]

I am wondering if it is obvious that there are two separate error messages

[brianteeman]

Perhaps adding this divider line helps?

.alert-message:not(:first-of-type) {
    border-top: 1px solid var(--alert-accent-color);
}

[infograf768]

Looks good. Will test tomorrow.

[infograf768]

It would look good for long messages in Installation but not really in admin.

[chmst]

In admin, multiple messages are really rare. And if they occur, it is worth to give them place. So it looks good for me.

[infograf768]

In fact I succeeded adding the border.
Can be tested during installation as well as in back-end or frontend.
Updated Testing instructions.

Please @chmst and @brianteeman test again.

[chmst]

I have tested this item ✅ successfully on 131d19a

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[Quy]

I have tested this item ✅ successfully on 131d19a

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/30401.}

[Quy]

RTC

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