test: Fix flaky Flush_BlocksCallingThread_TimesOut

[philipphofmann]

Make the test requirements less strict by removing the assert of the blocking duration and adding a test expectation timing out after 10 seconds to prevent hanging CI if the flush blocks longer.

The test failed here https://github.com/getsentry/sentry-cocoa/actions/runs/16743553141/job/47396825598

[philprime]

LGTM

[codecov]

❌ 3 Tests Failed:

Tests completed	Failed	Passed	Skipped
31825	3	31822	97

View the top 1 failed test(s) by shortest run time

SentryTests.SentryNetworkTrackerIntegrationTests::testGetRequest_SpanCreatedAndBaggageHeaderAdded

Stack Traces | 0s run time

.../Performance/Network/SentryNetworkTrackerIntegrationTests.swift:182 - XCTAssertTrue failed

View the full list of 2 ❄️ flaky tests

iOS_SwiftUI_UITests.FeedbackUITests::testWidgetDisplayInSwiftUIApp

Flake rate in main: 50.00% (Passed 2 times, Failed 2 times)

Stack Traces | 0s run time

.../iOS-SwiftUI/iOS-SwiftUI-UITests/FeedbackUITests.swift:14 - Failed to get matching snapshots: Timed out while evaluating UI query.

iOS_SwiftUI_UITests.LaunchUITests::testNoNewTransactionForSecondCallToBody

Flake rate in main: 12.50% (Passed 14 times, Failed 2 times)

Stack Traces | 0s run time

.../iOS-SwiftUI/iOS-SwiftUI-UITests/LaunchUITests.swift:36 - Failed to tap "Form Screen" Button: Timed out while evaluating UI query.

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[philipphofmann]

Unrelated unit and ui tests failed. I'm still merging this as a rerun would be a waste of time.