docs(auth): fix function name shadowing

Author: DoctorJohn

docs/auth/usage/index.md

@@ -58,13 +58,13 @@ function App() {
   const [user, setUser] = useState();
 
   // Handle user state changes
-  function onAuthStateChanged(user) {
+  function handleAuthStateChanged(user) {
     setUser(user);
     if (initializing) setInitializing(false);
   }
 
   useEffect(() => {
-    const subscriber = onAuthStateChanged(getAuth(), onAuthStateChanged);
+    const subscriber = onAuthStateChanged(getAuth(), handleAuthStateChanged);
     return subscriber; // unsubscribe on unmount
   }, []);