fix erroneous async component in integration test (#69760)

This component is used in Pages which doesn't support async components.
It silently worked because React 19 was used in pages but breaks in
React 18.

test/integration/module-id-strategies/components/CustomComponent.tsx

@@ -1,6 +1,6 @@
 import React from 'react'
 
-async function CustomComponent() {
+function CustomComponent() {
   return (
     <div>
       <h1>the content of a dynamic component</h1>