Fix integration tests for Windows (#16693)

The Nuxt preview server always starts on port 3000 even if that port is
taken. With the added tests in #16631 there is now a higher chance these
ports are already taken since e.g. react router prefers to start at port
3000 and so do other servers.
This PR changes this so that we assign a random port inside the test
instead.

## Test plan

- Ensure Windows CI is green again

integrations/vite/nuxt.test.ts

@@ -76,7 +76,9 @@ test('dev mode', SETUP, async ({ fs, spawn, expect }) => {
 
 test('build', SETUP, async ({ spawn, exec, expect }) => {
   await exec('pnpm nuxt build')
-  let process = await spawn('pnpm nuxt preview', {
+  // The Nuxt preview server does not automatically assign a free port if 3000
+  // is taken, so we use a random port instead.
+  let process = await spawn(`pnpm nuxt preview --port 8724`, {
     env: {
       TEST: 'false',
       NODE_ENV: 'development',