fix: #3614993 AjaxRenderer::renderResponse() triggers "Undefined array key...

Maxime Rouxrequested to merge
issue/drupal-3614993:3614993-ajaxrendererrenderresponse-triggers-undefined into main

fix: #3614993 AjaxRenderer::renderResponse() triggers "Undefined array key #attached" when render array has no attachments

Closes #3614993

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