Test `test_isolation_cookies` is flaky

[vdusek]

https://github.com/apify/crawlee-python/actions/runs/20305397716/job/58321314331?pr=1623

FAILED tests/unit/crawlers/_playwright/test_playwright_crawler.py::test_isolation_cookies[with use_incognito_pages] - AssertionError: assert '8GZOhlEWXO' == '3wZC3zF61j'
  - 3wZC3zF61j
  + 8GZOhlEWXO
=========== 1 failed, 1591 passed, 22 skipped in 334.06s (0:05:34) ============

https://github.com/apify/crawlee-python/actions/runs/20743217258/job/59554519720

FAILED tests/unit/crawlers/_playwright/test_playwright_crawler.py::test_isolation_cookies[without use_incognito_pages] - AssertionError: assert {} == {'a': '1'}
  
  Right contains 1 more item:
  {'a': '1'}
  
  Full diff:
  + {}
  - {
  -     'a': '1',
  - }
============ 1 failed, 1603 passed, 12 skipped in 333.47s (0:05:33) ============

[vdusek]

Test is still flaking after @pytest.mark.run_alone was added in #1733.

Recent failure on macOS-latest / Python 3.13:
https://github.com/apify/crawlee-python/actions/runs/24967827855/job/73105582975?pr=1857

FAILED tests/unit/crawlers/_playwright/test_playwright_crawler.py::test_isolation_cookies[without use_incognito_pages] - AssertionError: assert {} == {'a': '1'}

Mitigated for now with @pytest.mark.flaky(reruns=3) — root cause still not understood.

cc @Pijukatel