Support displaying a message that correctly validates file uploads for the Gin theme.

Is this something that should be fixed in Gin theme?

On 🐛 Incorrect display of message when validating uploaded files using Gin Admin Theme Closed: works as designed people say that IMCE is required to reproduce this, but your steps to reproduce seem to refute that. Is IMCE required to reproduce?

I can reproduce it, and it doesn't need IMCE. Is there something Gin theme could do to fix this?

The Gin message template (https://git.drupalcode.org/project/gin/-/blame/8.x-3.x/templates/misc/st...) includes a button tag:

<button type="button" class="button button--dismiss js-message-button-hide" title="{{ 'Hide'|t }}">
          <span class="icon-close"></span>
          {{ 'Hide'|t }}
</button>

The message is intended to be displayed within the $form['#prefix'] property. However, this property does not allow the display of button tags. Therefore, the message is validated and displayed without the button tag.

Essentially, Gin theme wants to make this form validation message dismissible whereas core themes like Claro do not, which is why we don't see this problem with Claro.