Fix flaky test (vercel#35951)

Failed here: https://github.com/vercel/next.js/runs/5855144575?check_suite_focus=true#step:9:1795

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`

test/integration/react-streaming-and-server-components/test/rsc.js

@@ -109,13 +109,15 @@ export default function (context, { runtime, env }) {
     expect(content).toContain('component:index.server')
 
     await browser.waitForElementByCss('#goto-streaming-rsc').click()
-    await new Promise((res) => setTimeout(res, 1500))
+
+    // Wait for navigation and streaming to finish.
+    await check(
+      () => browser.elementByCss('#content').text(),
+      'next_streaming_data'
+    )
     expect(await browser.url()).toBe(
       `http://localhost:${context.appPort}/streaming-rsc`
     )
-
-    content = await browser.elementByCss('#content').text()
-    expect(content).toContain('next_streaming_data')
   })
 
   it('should handle streaming server components correctly', async () => {