Fix: incorrect sample code in documentation related to Server action (#6445)

* Fix: component not returned

* Fix: missing function statement

Author: nonoakij

src/content/reference/react-dom/hooks/useFormStatus.md

@@ -38,7 +38,7 @@ function Submit() {
   return <button disabled={status.pending}>Submit</button>
 }
 
-export default App() {
+export default function App() {
   return (
     <form action={action}>
       <Submit />

src/content/reference/react/use-server.md

@@ -115,11 +115,13 @@ async function requestUsername(formData) {
   // ...
 }
 
-export default App() {
-  <form action={requestUsername}>
-    <input type="text" name="username" />
-    <button type="submit">Request</button>
-  </form>
+export default function App() {
+  return (
+    <form action={requestUsername}>
+      <input type="text" name="username" />
+      <button type="submit">Request</button>
+    </form>
+  );
 }
 ```