form: fix the bottom margin of the siret element

app/assets/stylesheets/new_design/forms.scss

@@ -335,6 +335,13 @@
     }
   }
 
+  .siret-info {
+    margin-top: -$default-fields-spacer;
+    margin-bottom: $default-fields-spacer;
+    // Ensure the bottom-margin is not collapsed when the element is empty
+    min-height: 1px;
+  }
+
   .send-wrapper {
     display: flex;
     width: 100%;

app/views/shared/dossiers/editable_champs/_siret.html.haml

@@ -1,11 +1,10 @@
 = form.text_field :value,
   placeholder: champ.libelle,
-  class: 'small-margin',
   data: { remote: true, debounce: true, url: champs_siret_path(form.index), params: { champ_id: champ&.id }.to_query, spinner: true },
   required: champ.mandatory?,
   pattern: "[0-9]{14}",
   title: "Le numéro de SIRET doit comporter exactement 14 chiffres"
 .spinner.right.hidden
-%div{ class: "siret-info-#{form.index}" }
+.siret-info{ class: "siret-info-#{form.index}" }
   - if champ.etablissement.present?
     = render partial: 'shared/dossiers/editable_champs/etablissement_titre', locals: { etablissement: champ.etablissement }