Check if classes could be added to class key instead of the generic attributes key

[dmolineus]

grid/src/Component/ContentElement/GalleryElement.php

Line 366 in d268e49

$cell->picture['attributes'] = 'class="img-fluid figure-img img-thumbnail"';

https://github.com/contao/contao/blob/0236382bf085f0a210409957c4b9c70c184f810b/core-bundle/src/Resources/contao/templates/picture/picture_default.html5#L11

[dmolineus]

Fixed with 23d4436