fix(tests): update combobox tests to wait for listbox visibility

Replace getByRole with findByRole to properly wait for the listbox
element to become visible after the CSS transition completes

Author: rossnelson

src/lib/holocene/combobox/combobox.stories.svelte

@@ -140,7 +140,8 @@
     const canvas = within(canvasElement);
     const combobox = canvas.getByTestId(id);
     await userEvent.type(combobox, 'E');
-    const menu = canvas.getByRole('listbox');
+    // Wait for the listbox to appear since it may have a transition
+    const menu = await canvas.findByRole('listbox');
     expect(menu).toBeInTheDocument();
   }}
 />
@@ -153,7 +154,8 @@
 
     await userEvent.type(combobox, 'one');
 
-    const menu = canvas.getByRole('listbox');
+    // Wait for the listbox to appear since it may have a transition
+    const menu = await canvas.findByRole('listbox');
 
     expect(menu).toBeInTheDocument();