test: Deflake test_error_handler_can_access_page on Windows CI

[vdusek]

test_error_handler_can_access_page fails intermittently on the Windows CI runner (example run). Under xdist load, Playwright's Page.goto occasionally fails with net::ERR_NO_BUFFER_SPACE before the page is navigated. That attempt's error handler then receives a BasicCrawlingContext (recorded as None) instead of a PlaywrightCrawlingContext, so the exact-list assertion [HELLO_WORLD, HELLO_WORLD] breaks with [None, HELLO_WORLD].

The crawler behaves correctly here (it retries, and a non-navigated attempt legitimately yields a basic context), so this is a test flake, not a product bug. The same net::ERR_NO_BUFFER_SPACE failure is already documented for three sibling tests (test_resource_management, test_adaptive_crawling_pre_nav_change_to_context, test_stagehand_browser_controller), which handle it with @pytest.mark.flaky(reruns=3).

Rather than retry, this makes the assertion robust to spurious pre-navigation failures: it ignores attempts that never reached the page (None) and asserts that at least one attempt did, and that every attempt that did exposes the page HTML. Removes the test's sensitivity to the flake deterministically while preserving what it verifies (that the error handler can read the page). No product code changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.34%. Comparing base (b850cd6) to head (1513919).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2018      +/-   ##
==========================================
- Coverage   93.36%   93.34%   -0.02%     
==========================================
  Files         179      179              
  Lines       12488    12488              
==========================================
- Hits        11659    11657       -2     
- Misses        829      831       +2     

Flag	Coverage Δ
unit	93.34% <ø> (-0.02%)	⬇️

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