Fix Server Function signature and two typos in 'use server' reference

requestUsername is passed to useActionState but declared as
requestUsername(formData). useActionState calls the action with the
previous state as the first argument, so formData ends up null and
formData.get('username') throws. The useActionState reference already
covers this under "My Action cannot read form data".

Also drop a stray semicolon in the LikeButton example, where it sits in
the fragment's children and renders as text, and remove a duplicated
word in the RSC banner so it matches use-client.md.

Author: BlackHatMan

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

@@ -5,7 +5,7 @@ titleForTitleTag: "'use server' directive"
 
 <RSC>
 
-`'use server'` is for use with [using React Server Components](/reference/rsc/server-components).
+`'use server'` is for use with [React Server Components](/reference/rsc/server-components).
 
 </RSC>
 
@@ -139,7 +139,7 @@ To update the UI based on the result of a Server Function while supporting progr
 // requestUsername.js
 'use server';
 
-export default async function requestUsername(formData) {
+export default async function requestUsername(prevState, formData) {
   const username = formData.get('username');
   if (canRequest(username)) {
     // ...
@@ -199,7 +199,7 @@ function LikeButton() {
   return (
     <>
       <p>Total Likes: {likeCount}</p>
-      <button onClick={onClick} disabled={isPending}>Like</button>;
+      <button onClick={onClick} disabled={isPending}>Like</button>
     </>
   );
 }