fix: give buttons the input box model so they align with fields

templates/booking/_participant_form.html.twig

@@ -697,11 +697,11 @@
             </h3>
             <div class="mb-4">
                 {{ form_label(form.voucherCode) }}
-                <div class="flex items-center gap-2">
-                    <div class="grow">
+                <div class="flex items-end gap-2">
+                    <div class="grow min-w-0">
                         {{ form_widget(form.voucherCode) }}
                     </div>
-                    <button type="button" class="button button--secondary"
+                    <button type="button" class="button button--secondary shrink-0 whitespace-nowrap"
                         {% for name, value in voucherHx %} {{ name }}="{{ value }}"{% endfor %}>
                         Code einlösen
                     </button>