[test-utils] testing for prerender build

Describe the feature

If we have a special implementation in the prerender environment, we may want to test it with its built from time to time.
case: https://github.com/nuxt-modules/i18n/pull/1733

In @nuxt/test-utils setup, we can override the nuxtConfig option with _generate: true, which is equivalent to nuxi generate.

However, the server in @nuxt/test-utils is not yet ready to run a server for the prerender environment, so the test will stop with the following log output:

Error: Cannot find module '/path/to/nuxt/i18n/specs/fixtures/basic/.nuxt/ubpgju/output/server/index.mjs'
    at Function.Module._resolveFilename (node:internal/modules/cjs/loader:933:15)
    at Function.Module._load (node:internal/modules/cjs/loader:778:27)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:17:47 {

Additional information

• Would you be willing to help implement this feature?
• Could this feature be implemented as a module?

Final checks

• Read the contribution guide.
• Check existing discussions and issues.

Start in the @nuxt/test-utils setup and trace how the nuxtConfig _generate: true option invokes nuxi generate and then starts the server. Reproduce the missing output/server/index.mjs failure, then verify that a prerender test can run without stopping on that missing module.