Fix nested example setup with create-next-app

[ijjk]

Noticed in #45387 we aren't properly setting up nested examples due to not stripping to the right level so this ensures we handle that case properly.

[ijjk]

Failing test suites

Commit: f0c8a79

pnpm testheadless test/e2e/app-dir/metadata/metadata.test.ts

• app dir - metadata > metadata > basic > should apply metadata when navigating client-side

Expand output

● app dir - metadata › metadata › basic › should apply metadata when navigating client-side

page.waitForSelector: Timeout 2000ms exceeded.
=========================== logs ===========================
waiting for locator('#basic')
============================================================

  329 |     return this.chain(() => {
  330 |       return page
> 331 |         .waitForSelector(selector, { timeout, state: 'attached' })
      |          ^
  332 |         .then(async (el) => {
  333 |           // it seems selenium waits longer and tests rely on this behavior
  334 |           // so we wait for the load event fire before returning

  at lib/browsers/playwright.ts:331:10
  at Object.<anonymous> (e2e/app-dir/metadata/metadata.test.ts:275:11)

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