[2799] Fix node style in diagram pre-layout

Bug: #2799
Signed-off-by: Florian ROUËNÉ <florian.rouene@obeosoft.com>

CHANGELOG.adoc

@@ -154,6 +154,7 @@ Now, for a multi-valued feature, the values are properly displayed and the delet
 - https://github.com/eclipse-sirius/sirius-web/issues/2901[#2901] [diagram] Fix an issue where the connectionLine could be stuck on invalid nodes.
 - https://github.com/eclipse-sirius/sirius-web/issues/2940[#2940] [diagram] Fix an issue where the diagram palette would render with no tools.
 - https://github.com/eclipse-sirius/sirius-web/issues/2986[#2986] [portal] Prevent a portal from containing itself
+- https://github.com/eclipse-sirius/sirius-web/issues/2799[#2799] [diagram] Remove the unwanted space between the header and first element in list node
 
 === New Features
 

packages/diagrams/frontend/sirius-components-diagrams-reactflow/src/renderer/layout/layout.tsx

@@ -93,6 +93,7 @@ export const prepareLayoutArea = (
       const element: JSX.Element = createElement('div', {
         id: `${node.id}-label-${index}`,
         key: `${node.id}-label-${index}`,
+        role: 'button', // role applied by react flow
         children,
       });
       labelElements.push(element);