fix(flags): fix/refactor flaky launchdarkly tests

[aliu39]

Fixes flakes (example) caused by background processes in LDClient trying to connect to a non-existent server (we're mocking the flag data through TestData).

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
13784	1	13783	4132

View the top 1 failed tests by shortest run time

tests.test_transport test_transport_works[threads-False-gzip-0-True-flush-False]

Stack Traces | 2.52s run time

tests/test_transport.py:187: in test_transport_works
    assert capturing_server.captured
E   AssertionError: assert []
E    +  where [] = <CapturingServer(<class 'tests.test_transport.CapturingServer'>, started 140302203479808)>.captured

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[aliu39]

Looks like anthropic-pinned is failing now for 3.7 and 3.8: https://github.com/getsentry/sentry-python/actions/runs/12508778454/job/34899363812?pr=3896