Fix flaky redbox expectation in unstable_after e2e test (#66490)

test/e2e/app-dir/next-after-app/index.test.ts

@@ -361,6 +361,7 @@ describe.each(runtimes)('unstable_after() in %s runtime', (runtimeValue) => {
           '/invalid-in-client'
         )
         try {
+          expect(await session.hasRedbox()).toBe(true)
           expect(await session.getRedboxSource(true)).toMatch(
             /You're importing a component that needs "?unstable_after"?\. That only works in a Server Component but one of its parents is marked with "use client", so it's a Client Component\./
           )