[TwigBridge] Fix HTML for translatable custom-file label in Bootstrap 4 theme
[TwigBridge] Fix HTML for translatable custom-file label in Bootstrap 4 theme

Bootstraps allows to translate the label of the button of a custom-file
input with SCSS variables depending on the lang attribute of the
*input*.
This attribute was set on the label instead and thus had no effect.

symfony/twig-bridge,symfony/TwigBridge