Fix code example in React-19 useOptimistic section (#6781)

should assign the result of updateName

Co-authored-by: Tim Neutkens <tim@timneutkens.nl>

src/content/blog/2024/04/25/react-19.md

@@ -211,7 +211,7 @@ function ChangeName({currentName, onUpdateName}) {
   const submitAction = async formData => {
     const newName = formData.get("name");
     setOptimisticName(newName);
-    await updateName(newName);
+    const updatedName = await updateName(newName);
     onUpdateName(updatedName);
   };