fix(ts): correct return type on AppRouteHandlerFnContext

Author: balazsorban44

packages/next-auth/src/lib/types.ts

@@ -21,7 +21,7 @@ export type AppRouteHandlerFn = (
    * dynamic route).
    */
   ctx: AppRouteHandlerFnContext
-) => unknown
+) => void | Response | Promise<void | Response>
 
 export type AppRouteHandlers = Record<
   "GET" | "POST",