Flaky basics form submission test on GitHub Actions due to extra CSS chunk

Describe the bug

The packages/kit/test/apps/basics Playwright suite intermittently fails on Routing › responds to <form method="GET"> submission without reload. When a CSS chunk (e.g. _app/immutable/assets/0.DylTJ_5d.css) is fetched during form submission, the test fails because it expects no additional network requests after the form submit.
This likely occurs due to route-level CSS code-splitting in SvelteKit. The small <style> in src/routes/+layout.svelte is extracted into a separate asset whenever a new route is added or moved, even if that route defines no styles.
It appears that the outcome depends on whether that CSS chunk was cached by a previous test run, causing the test to alternate between passing and failing.

Reproduction

No external reproduction required
reproducible in SvelteKit CI (GitHub Actions).

Logs

System Info

System:
  OS: Linux (GitHub Actions CI)

Severity

annoyance

Additional Information

No response

Start in the packages/kit/test/apps/basics Playwright suite with Routing › responds to

submission without reload, then inspect src/routes/+layout.svelte and the route-level CSS behavior described in the issue. Reproduce the GitHub Actions failure and verify that the test remains stable without an unexpected CSS chunk request after form submission.